Dioxins, a class of chemical contaminants produced in both natural and industrial processes, were discovered in the late 1950s and have been extensively studied since the early 1970s. The majority of studies have focused on the most toxic congener, 2,3,7,8-TCDD, simply called dioxin,¹ with much toxicology, biochemistry, and epidemiology research having been aimed at determining its effects on humans, in particular its carcinogenic effects. Nevertheless, despite thirty years of intensive research, exactly how dangerous dioxin is remains a controversial issue. In 1997 the International Agency for Research on Cancer (IARC) classified TCDD as a group 1 carcinogen based on limited