The toxicology and epidemiology of dioxin is a broad subject, so I will very briefly review the animal toxicology, then the early studies we conducted here in Missouri and finally other human aspects of TCDD exposure. Figure i is the chemical structure of 2,3,7,8 tetrachlorodibenzodioxin. There are many other chlorinated dibenzodioxin isomers, and the term dioxin is used very loosely. For some isomers, the chlorines are not in the 2,3,7,8 position, but in other places. Some of those isomers are not nearly as toxic as the TCDD; an important point to remember. For instance, the octochlorodibenzodioxin, which is completely chlorinated, has an LD50 of about 2 grams per kilogram body weight. Table i. Chlorinated compounds in samples of soil and oil