The effects of cytochalasin D on chick embryos were analyzed in the present study. Cytochalasin D was dissolved in DMSO and injected into embryonating chicken eggs at dosages ranging from 0.001 to 0.014 mg per egg. The injections were made into the air sacs of eggs at days 0, 1, 2 and 3 of incubation. The volume of each injection was 0.1 ml per egg. In all, 864 chicken eggs were used for this study. All embryos were examined on day eleven. The following malformations were observed: exencephaly, microphthalmia, everted viscera, body hemorrhage, edema, anophthalmia and a reduced body size. The dose-response relationship was observed in all of the groups tested. The results of the present study indicate that cytochalasin D is embryolethal and has some tendency to cause malformations in the chick embryos tested.