We have developed a short-term bioassay for analysis of the teratogenic effects of dioxin. Fertile chicken eggs were injected with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or control oil at the start of incubation. Chick embryos were sacrificed following 1,2,3 and 4 days of incubation, fixed, developmentally staged and analyzed for teratogenic effects. No significant effects were observed after one day of incubation. However, by the second day of incubation (embryonic day 2, or E2) several abnormalities were observed including asymmetrical somites and heart malformations. By E3 and E4, observed effects included malformed visceral arches, decreased vitelline vasculature, and variations in the chronological development within a given embryo of certain developmental indicators including the number of somites, the curvature, the limb buds and the allantois. After testing both airsac and yolk injections, we found that similar results were found using either method.