The objective of this study was to determine the development toxicity potential of hydroquinone in the rat. Pregnant Crl: COBS 'CD' (SD) BR rats were given 0, 30, 100 or 300 mg/kg of hydroquinone by gavage on the 6th through the 15th days of gestation and fetuses were examined near term. Maternal toxicity was seen as a slight but statistically significant reduction in body weight gain and feed consumption during the treatment period in the dams given 300 mg/kg hydroquinone. A few spontaneous malformations were seen, but no compound-related teratogenic effects were found. Minor soft tissues and skeletal changes, variations commonly found in developmental toxicity studies, did not occur at a significantly higher incidence in the treated groups than in the control group. Reproductive indices of the hydroquinone dams were comparable to the controls. A reduction in mean fetal body weight seen at the high dose level (300 mg/kg) correlated with the reduced body weight seen in the dams at this dose level. In conclusion, doses as high as 300 mg/kg hydroquinone did not produce teratogenic effects, other embryotoxicity, or fetotoxicity in the rat.