The developmental toxic effect of hydroquinone (HQ) was evaluated in chick embryos after 72 and 96 hour of incubation. HB was injected into the air sacs of the eggs at doses ranging from 0.0625 to 40 mu g per egg. On the 15 th day of incubation, live embryos including controls were removed from the eggs and examined for gross malformations and body hemorrhage. hours The LD(50) values for HQ at 72 and 96 hours of incubation were 8.59 and 15.63 mu g per egg, respectively. HQ produced gross malformations such as body hemorrhage, curled claws, everted viscera, defective beak, exencephaly and monophtalmia in developing chick embryos at dosages ranging from 20 to 0.0625 mu g per egg in both groups. The various types of malformations and their incidences in both groups were higher in comparison with the controls, but were not statistically significant. At no concentration did malformations occur greater, than 35 percent for both 72 and 96 hours of incubation. The results of this study reveal that HQ is embryo toxic at higher doses and that teratogenic potential of HQ is unremarkable.