The following are facts about some of the chemical and biological weapons experts say Iraq probably has or could quickly make, according to U.N. reports, former weapons inspectors and weapons experts:
WHAT IT IS: The most toxic of chemical weapons, VX is a sticky, colorless liquid that evaporates slowly into a colorless, odorless gas.
WHAT IT DOES: VX interferes with the body's nerve impulses, causing convulsions and paralysis of the lungs and blood vessels. Victims essentially choke to death. A dose of 10 milligrams on the skin is enough to kill.
WHAT IRAQ HAD: Iraq acknowledged making 3.9 tons of VX, which it said it destroyed. U.N. inspectors estimated Iraq had the means to make more than 200 tons of VX and never found definitive proof Iraq had destroyed its supply.
WHAT IT IS: A nerve agent like VX, sarin is a liquid that evaporates quickly.
WHAT IT DOES: Like VX, sarin causes convulsions, paralysis and asphyxiation. The Aum Shinrikyo cult used sarin in attacks on in the Tokyo subway system in 1995 that killed 12 people.
WHAT IRAQ HAD: Iraq first told U.N. inspectors it had made 812 tons of sarin, then said it had made 790 tons. Iraq also produced binary weapons: bombs carrying two separate chemicals that when combined in an explosion, produce sarin. Iraq acknowledged making thousands of rockets, artillery shells and bombs containing sarin and used the chemical during its war with Iran in the 1980s and is believed to have used it against Kurdish Iraqi civilians.
WHAT IT IS: A colorless liquid at room temperature, mustard agent evaporates into a gas that may be odorless or smell like mustard or rotten onions.
WHAT IT DOES: Mustard agent begins dissolving tissues on contact, causing skin injuries similar to burns, as well as damage to lungs and eyes. Mustard agent usually is not fatal but can cause blindness, lung problems and other injuries that can be painful for decades. It was first used in World War I.
WHAT IRAQ HAD: Iraq gave two figures of how much mustard gas it produced: 3,080 tons and 2,850 tons. Iraq acknowledged extensive use of mustard gas against Iran during the Iran-Iraq war in the 1980s. Iraq told the U.N. it misplaced 550 mustard-filled artillery shells after the 1991 Gulf War.
WHAT IT IS: Bacillus anthracis, a hardy bacteria that causes illness in livestock and humans.
WHAT IT DOES: There are three types of anthrax infection: skin lesions, gastrointestinal infection and lung, or inhalation, anthrax. The deadliest -- and the one weapons are designed to produce -- is inhalation anthrax, which starts with flu-like symptoms but escalates to fill the lungs with fluid, causing death. Just a few tiny anthrax spores are enough to cause a deadly infection in some vulnerable people. The anthrax attacks last year showed that antibiotics, if given early, can eliminate the infection, and the U.S. military has a program to vaccinate its soldiers against the disease.
WHAT IRAQ HAD: Iraq acknowledged making 2,200 gallons of anthrax spores -- enough to kill millions if delivered effectively -- but U.N. inspectors determined Iraq could have made at least three times that much. As many as 16 missile warheads filled with anthrax are missing. Iraq also was working in the 1990s to produce a deadlier dry, powdered form of anthrax, inspectors say. That powder could be sprayed from aircraft, put into missile warheads or given to terrorists, inspectors say.
WHAT IT IS: A poison produced by the Clostridium Botulinum bacteria, botulinum toxin is one of the deadliest substances known.
WHAT IT DOES: In small doses, such as those in food contaminated with the bacteria, it can cause stomach cramps, diarrhea, blurry vision and muscle weakness which can advance to paralysis and death. If the toxin is applied in pure form -- especially if it is inhaled -- the paralysis and death can be very rapid. About 70 billionths of a gram is enough to kill if inhaled.
WHAT IRAQ HAD: Iraq acknowledged making nearly 5,300 gallons of botulinum toxin, most of which was put into missile warheads and other munitions. At least five missile warheads filled with botulinim toxin are missing.
WHAT IT IS: A poison produced by the Aspergillus flavus fungus and related fungi that grow on grain.
WHAT IT DOES: Aflatoxin is a potent carcinogen that causes liver cancer. In large doses it can cause abdominal pain, swelling of the lungs and brain, convulsions, coma and death.
WHAT IRAQ HAD: Iraq acknowledged making more than 520 gallons of aflatoxin and putting it into missile warheads and bombs. At least four aflatoxin-filled missile warheads are missing.