Ranitidine hydrochloride, a histamine H2-receptor antagonist, was orally given to pregnant rabbits of Japanese White strain from day 6 to 18 of gestation at doses of 25, 100 and 400 mg/kg/day, as ranitidine base, and teratogenicity of the drug was studied. The results were as follows: (1) At dose of 400 mg/kg/day, ranitidine hydrochloride showed no effects on dams, excepting slight suppression in body weight gain in early period of administration. (2) In fetuses, no effects of ranitidine hydrochloride on fetal growth, sex ratio, viability and degree of ossification were observed. (3) External and visceral abnormalities were observed 5, 3, 3 and 4 fetuses in control, 25, 100 and 400 mg/kg/day groups, respectively, but there was no significant difference of the incidence ratio in the treated groups from control, and was no increase in the same type of abnormality. Ranitidine hydrochloride induced no increase in incidence of visceral and skeletal variations. Therefore it was concluded that ranitidine hydrochloride had no teratogenic effect on rabbits at dose of 400 mg/kg/day or lower than that.