Agent Orange is the name used by the U.S. military for a 1:1 mixture of the herbicides 2,4-D and 2,4,5-T. The name, Agent Orange, was derived from the orange stripe on drums in which the herbicide was stored.

This image was copied with permission from Gary Moore.

Large quantities were sprayed in Vietnam to defoliate trees that might hide the enemy. Fears that Agent Orange can cause human illness stem from the presence in it of a contaminant called TCDD (short for 2,3,7,8-tetrachlorodibenzo-para-dioxin). TCDD is only one of a family of substances called dioxins, but it is the one that has gained the greatest notoriety. TCDD is commonly referred to as dioxin.

Dioxin is produced as an undesired contaminant during the manufacture of 2,4,5-T. Tests show that it is a potent teratogen for some laboratory animals; that is, exposure of pregnant females to exceedingly small amounts of dioxin causes malformed offspring.