Nicotine, administered at a dose of 100 micrograms/kg/day from day 14 of gestation, did not affect maternal food intake, weight gain, length of gestation, litter size or fetal development; however, a daily dose of 1 mg/kg led to smaller litter size and higher incidence of stillbirth. Continued maternal administration of nicotine (100 micrograms/kg/day) until 12 days post partum did not affect newborn growth (body weight and length and size of heart and lung) during the first week after birth; during the second week, however, the nicotine-treated group lagged behind the controls. The stomachs of pups of nicotine-treated rats contained less food than those of controls; this difference increased with age, becoming more than 40% at 12 days. We suggest that lower milk production of nicotine-treated rats interferes with the normal development of the offspring during periods of rapid growth.