White Leghorn chick embryos were used to investigate the embryotoxicity and teratogenicity of 25 and 50% Buckley's formocresol. Embryos were injected at 48 h and sacrificed on the ninth day of incubation. The percentage of mortality of sham and vehicle controls was 4.8 and 17.7%, respectively, whereas eggs injected with 25 and 50% formocresol displayed a 40 and 100% mortality rate. Gross morphological abnormalities, weights, and crown-rump lengths were determined, demonstrating that Buckley's formocresol is embryotoxic and teratogenic in chick embryos. Gross morphological changes were noted to include cranial hematomas, facial abnormalities, eye and beak deformities as well as alterations in feather germ appearance. Histological changes included alterations in the organization of the eyes, and formation of the beak, palate, vasculature, musculature, cartilage, and bone. Moreover, experimental embryos displayed a retardation of development in that they lagged behind their controls by approximately 24 to 36 h.