Sept. 18: Envelopes containing letters and granular substances are sent to NBC News in New York and the New York Post. Both are mailed from Trenton, N.J.

Sept. 22: Editorial page assistant at New York Post who opens letters to the editor notices blister on her finger. She later tests positive for skin form of anthrax.

Sept. 26: Maintenance worker at Trenton regional post office in Hamilton, N.J., visits physician to have lesion on arm treated.

Sept. 27: Teresa Heller, letter carrier at West Trenton post office, develops lesion on her arm.

Sept. 28: Erin O'Connor, assistant to NBC News anchor Tom Brokaw, notices a lesion.

The 7-month-old son of an ABC producer in Manhattan spends time at the network offices. He develops a rash, and is hospitalized with an unknown ailment soon after the visit. He is later diagnosed with cutaneous anthrax.

Sept. 30: Bob Stevens, photo editor at supermarket tabloid The Sun in Boca Raton, starts to feel ill.

Oct. 1: Erin O'Connor, the NBC assistant to anchor Tom Brokaw, goes to her doctor with a low-grade fever and a bad rash and is prescribed the antibiotic Cipro.

Ernesto Blanco, 73, an American Media Inc. mailroom employee, is hospitalized with pneumonia.

Oct. 2: At 2:30 a.m., American Media Inc. photo editor Stevens arrives at JFK Medical Center in Atlantis with 102-degree fever, vomiting and confusion. He deteriorates rapidly.

Oct. 3: Doctors determine Stevens, 63, has anthrax. He is on a respirator, being treated with intravenous penicillin.

In New Jersey, Heller, the West Trenton post office letter carrier, is hospitalized and a biopsy is performed.

Oct 4: AMI calls the U.S. Centers for Disease Control and Prevention to ask whether its Boca Raton headquarters should be evacuated. The CDC says no, and everyone continues working as usual at AMI. That afternoon, JFK Medical Center along with the Florida Department of Health's Dr. Steven Wiersma call a news conference to confirm that a patient has anthrax. They stress that it is a public health investigation and they believe it is an isolated case.

Oct. 5: Teams from the CDC fan out to Stevens' home and office. At JFK's intensive care unit, Stevens is pronounced dead, becoming the first anthrax fatality in the United States since 1976.

Oct. 7: At 7 p.m. the CDC notifies AMI that they intend to seal the building because test samples have shown anthrax spores on Stevens' computer keyboard and in the nasal passages of Ernesto Blanco, an AMI employee who delivered mail to other workers there.

Oct. 8: In Miami, the family of Ernesto Blanco is notified that Blanco has tested positive for anthrax exposure. He has no symptoms of anthrax infection. Employees of AMI line up at the Delray Health Center to be tested and to receive a two-week supply of antibiotics

Oct. 9: Letters containing anthrax addressed to U.S. Senate Majority Leader Tom Daschle and Sen. Patrick Leahy are postmarked in Trenton, N.J. The letters bear the same fictitious "Greendale School" return address and are written in all-capital block letters.

In New York, a skin biopsy is performed on the NBC employee.

In South Florida, the FBI says it found no traces of anthrax in the known places the Sept. 11 hijackers had stayed, or in Stevens' home or the places he frequented. Federal and state officials said they now believe the case is an isolated incident of "foul play." President Bush tries to assure anxious Americans that the Florida cases do not warrant national alarm.

Oct. 10: Federal investigators announce that a third AMI employee has tested positive for anthrax exposure and that the AMI case has become a criminal investigation.

Oct. 11: Federal officials say they have found more anthrax spores in the AMI mailroom. Postal workers demand to be tested for anthrax exposure. The third AMI employee to test positive for anthrax exposure, Stephanie Dailey, 36, announces from her Boynton Beach home that she is on antibiotics and feels fine.

Oct. 12: In New York, the skin biopsy tests on the NBC employee reveals that she had been exposed to anthrax, making her the fourth confirmed exposure to the potential germ warfare agent at a media company. NBC offices are sealed off while investigators conduct tests. The letter to NBC's Brokaw from Trenton, N.J. containing the granular substance is tested.

Post officials believe on this day, the anthrax letter addressed to Sen. Leahy was misrouted and passed through a State Department mail facility in Sterling, Va., where a worker later developed inhalation anthrax.

Oct. 13: Five more employees of the Boca Raton tabloid publisher American Media Inc. test positive for the presence of anthrax bacteria. The employees are put on antibiotics and are not expected to develop the disease.

The threatening letter sent to Brokaw from Trenton, N.J. tests positive for anthrax. A second NBC News employee who handled the letter reports possible symptoms.

Oct. 14: The number of individuals exposed to anthrax grows to 12. Three new cases -- a police officer and two lab technicians involved in an investigation at NBC's New York headquarters -- test positive for the bacteria, Mayor Rudolph Giuliani announces.

Oct. 15: The nation's anthrax inquiry widens. The letter postmarked in Trenton, N.J. is opened in the Washington office of U.S. Senate Majority Leader Tom Daschle. It tests positive for anthrax.

Inspectors in Boca Raton confirm the presence of spores in the city's main post office.

In New York, ABC announces that the 7-month-old son of one of its producers was found to be infected with cutaneous anthrax. The boy had been at the network's offices in Manhattan on Sept. 28.

The Florida Department of Health announces that tests show Ernesto Blanco, an AMI mailroom employee, has contracted the inhaled form of anthrax. Earlier tests indicated he had only been exposed to anthrax spores.

Oct. 16: AMI says it probably destroyed the letter to its Boca office that contained anthrax. AMI management decides to abandon its headquarters.

U.S. Senate offices close as hundreds line up for tests. It is announced that the anthrax mailed to Senate Majority Leader Tom Daschle is a pure and highly potent version. Based on similarities in the handwriting on the envelope and the postmarks, the FBI links this letter to the one sent to NBC News.

Oct. 17: Congressional leaders arrange for an unprecedented shutdown of the House after 31 people test positive for exposure to anthrax; the number is later dropped to 28. Those exposed include workers in the offices of Senate Majority Leader Tom Daschle and Sen. Russell Feingold and Capitol Hill police officers.

New York Gov. George Pataki announces that anthrax has been found in his Manhattan office, but later tests came up negative.

Preliminary tests indicate the anthrax sent to New York and Florida is the same strain.

Oct. 18: The bacteria strikes the third major television network, forces the decontamination of two more South Florida post office buildings and is found in a package that originated in the United States and was delivered to Kenya.

An assistant to CBS News anchor Dan Rather and a New Jersey postal worker are diagnosed with the skin form of the disease in New York, making them the fifth and sixth Americans to come down with anthrax.

Oct. 19: A New York Post employee develops the skin-form of anthrax. A second New Jersey postal worker is diagnosed with the skin-form of anthrax, making him the eighth person nationwide to contract the disease.

Oct. 20: Anthrax spores are found in the Ford Office Building, where mail is processed for legislators in the House of Representatives. Also, a postal worker at the Brentwood post office in Washington D.C. is tested for anthrax.

Oct. 21: Thomas Morris Jr., 55, a Washington postal worker suspected of having inhalation anthrax, dies. Reports indicate that in a desperate 911 call hours before he died, the Washington mail sorter told a dispatcher that he suspected he had been exposed at work to an envelope containing lethal anthrax spores. His previous attempts to convince his supervisors and doctor that he had anthrax went unheeded.

The New York Post says its anthrax letter is almost identical to those sent to Brokaw and Daschle.

Oct. 22: The scope of the anthrax problem in Washington grows dramatically. Joseph Curseen, 47, a Washington postal worker, comes to the hospital with flu-like symptoms in the morning and dies of inhalation anthrax by evening, making him the second postal worker to die of anthrax.

Two more postal workers are hospitalized; nine others are ill with symptoms. Authorities test 2,200 workers.

Oct. 23: Anthrax is detected on a letter-opening machine that screens White House mail. Authorities confirm the two postal workers who died succumbed to anthrax. Three more workers are ill from inhaled anthrax -- two in Washington, one in New Jersey. Images of the three anthrax letters mailed from Trenton, N.J., are released; they are strongly similar. Ernesto Blanco, AMI mailroom worker diagnosed with inhaled anthrax, is released from the hospital after 23 days.

Oct. 24: Surgeon General David Satcher admits ``we were wrong'' not to respond more aggressively to tainted mail in Washington. Three new cases of suspected inhalation anthrax announced in Maryland suburbs, all linked to Daschle letter.

Oct. 25: An employee at the State Department's mail facility is hospitalized with anthrax and the Postal Service sets up spot checks at facilities nationwide.

Homeland Security Director Tom Ridge says the anthrax the Daschle letter was highly concentrated and made ``to be more easily absorbed'' by its victims.

The number of Americans taking antibiotics for possible anthrax exposure reaches 10,000.

Oct. 26: The Supreme Court building is ordered shut down for anthrax testing. Postal workers demand the closure of anthrax-tainted buildings in New York and Florida, with some union officials threatening to sue the Postal Service

Oct. 29: A 61-year-old worker at a Manhattan hospital tests positive for inhalation anthrax. She is in "very, very serious" condition and on a respirator, officials say.

New Jersey health authorities report a woman who handles mail for a private company there has cutaneous anthrax.

Small amounts of anthrax were found in the Supreme Court's basement mailroom and four other federal buildings in Washington.

Tests in Florida on cars used by two of the Sept. 11 hijackers found no traces of anthrax.

Oct. 30: Trace amounts of anthrax are found in the mailroom of the USDA Economic Research Service, and the head of the State Department's medical unit also says that anthrax spores are "probably all over" the two-block building.

U.S. Postal Service officials say anthrax spore traces have been found at a postal station in northwest Washington and in Dulles Station, Virginia.

Oct. 31: A New York City hospital worker becomes the fourth victim to die from inhalation anthrax. Kathy Nguyen, 61, worked in a medical supply room in the basement of the Manhattan Eye, Ear and Throat Hospital, in an area that once housed a mailroom.

In New Jersey, a major mail plant is shut down after a postal employee is suspected of having skin anthrax. In the nation’s capital, three post office centers that had been closed for decontamination are reopened.

Nov. 2: The director of the Federal Bureau of Investigation says that after weeks of investigation, the government has no idea who is behind the anthrax attacks, and he appeals to the public for help in solving the case.

Nov. 4 The FBI, criticized for its sluggish response to the widening anthrax crisis, begins testing hundreds of barrels of quarantined government mail at a Washington-area facility in search of undetected anthrax-laden letters. Health officials confirm more traces of anthrax in New York and Washington.

Nov. 6 No new anthrax cases are reported, and several buildings that had closed because of anthrax scares, including a New Jersey post office and a New York hospital, reopen.

Nov. 9:After three weeks of searching the American Media Inc. building for anthrax, federal officials dismantle the teams, leaving the Boca Raton site for its tabloid publisher to clean up.

The FBI says it is increasingly convinced that the person behind the recent anthrax attacks is a lone wolf within the United States who has no links to terrorist groups but is an "opportunist" using the Sept. 11 hijackings to vent his rage.

Nov. 10:Small amounts of anthrax are discovered in four new locations on Capitol Hill, including the Hart Building offices of Sens. Bob Graham, D-Fla., and Dianne Feinstein, D-Calif., but they do not threaten the health of anyone who worked or visited there, officials announce.

Nov. 12: Trace amounts of anthrax are found in the offices of three more senators, bringing to 11 the number of senators' suites found in recent days to be contaminated. The most recent discoveries were in the offices of Sens. Richard Lugar (R-Ind.), Barbara Boxer (D-Calif.) and Jon Corzine (D-N.J.). All 11 are in the Hart Senate office building, where an anthrax-filled letter was opened Oct. 15.

Nov. 17: Capitol police close two Senate office buildings to test for anthrax spores after investigators discover a contaminated letter addressed to Sen. Patrick Leahy, D-Vt. The letter was postmarked from Trenton, N.J., as was the one sent to Senate Majority Leader Tom Daschle, and contains similar handwriting, investigators said.

Nov. 20: A sample taken from a plastic evidence bag containing a still-unopened letter to Sen. Patrick Leahy contains at least 23,000 anthrax spores, enough for more than two lethal doses, a federal law enforcement official reports. Traces of the anthrax bacteria are also found in the office mailrooms of Sens. Edward Kennedy, D-Mass., and Christopher Dodd, D-Conn.

Nov. 21: Ottilie Lundgren, 94, of Oxford, Conn., dies of inhalation anthrax, baffling authorities who see no immediate connection between this rural town and bioterror attacks in New York, Washington and Florida. She is the fifth person to die of inhalation anthrax in less than two months.

Nov. 23: Anthrax tests in and around Ottilie Lundren's Connecticut home come back negative, further enshrouding in mystery her death from inhalation anthrax.

Chilean and U.S. officials confirmed the first reported case of a deadly strain of the bacteria in mail outside the United States. The Centers for Disease Control and Prevention in Atlanta confirmed on Thursday that a letter sent from Switzerland to Chile was tainted with anthrax. The letter had been sent to Dr. Antonio Banfi, a pediatrician at a children's hospital in Santiago.

Nov. 28: A state health lab in Miami confirms the presence of anthrax in a letter mailed from Zurich, Switzerland, to a pediatrics professor in Chile.

Dec. 6: A batch of mail being processed at a mail-handling facility set up in a courtyard of the Federal Reserve's headquarters tests positive for anthrax. Officials say the positive reading was obtained for a batch of mail containing about 100 to 150 letters and it had not been determined whether any of the letters actually contained anthrax spores or whether some of the mail had been contaminated by other letters.

Government scientists open the anthrax-laden letter sent to Sen. Patrick Leahy, D-Vt., and find it to be "virtually identical" to one mailed to a colleague, Senate Majority Leader Tom Daschle, D-S.D.

Dec. 7: Officials assure government workers that all federal mail is being irradiated to render any anthrax spores harmless.

Dec. 8: Employees of American Media Inc. in Boca Raton, the first place anthrax was discovered, end their two-month course of the antibiotic Cipro.