OBJECTIVE Our study was designed to test the hypothesis that maternally administered nicotine has significant effects on fetal hemodynamics and umbilical systolic/diastolic ratios. METHODS Nine pregnant ewes received maternal intravenous infusions of 10, 20, and 30 micrograms/kg/min of nicotine. Maternal and fetal blood pressure, heart rate, and uterine and umbilical blood flow were recorded. RESULTS Maternal intravenous administration of nicotine (10, 20, and 30 micrograms/kg/min of maternal body weight) produced significant (p < 0.05) increases in fetal blood pressure (2%, 11%, and 25%, respectively), decreases in fetal heart rate (0%, 8%, and 12%), and decreases in umbilical blood flow (0%, 0%, and 19%). Umbilical systolic/diastolic ratios increased slightly at the 30 micrograms/kg/min dose of nicotine, but these changes did not reach significance. Maternal blood pressure increased (10%, 25%, and 53%), and uterine vascular resistance increased (5%, 64%, and 344%) significantly (p < 0.05); uterine blood flow increased at the 10 micrograms/kg/min dose (+5%) and decreased by 23% and 42% at the highest two doses of nicotine. CONCLUSIONS Maternal nicotine administration in late-term pregnant sheep produced significant increases in fetal arterial blood pressure and umbilical vascular resistance, decreased fetal heart rate, and umbilical blood flow but did not significantly alter systolic/diastolic ratios.