The pyrazolone dye Orange B was given by gavage to pregnant Osborne-Mendel rats throughout gestation. Dose levels of 0, 15, 30, 100, 200, 400, or 700 mg/kg body weight were given daily. On gestation day 20, the females were killed and cesarean sections were performed. Feed consumption and maternal weight gain were not affected. No dose-related changes were seen in maternal clinical findings, implantations, fetal viability, or fetal size (weight and length). No compound-related effects were seen in sternebral development. No dose-related effect was seen in the incidence of skeletal variations in fetuses or in the number of litters containing fetuses with skeletal variations. Skeletal development, as measured by the average number of ossified vertebrae, was similar in all groups. No compound-related effects were seen in soft-tissue development.