The effects of intravenous cocaine on heart rate and blood pressure were studied in pregnant and oophorectomized nonpregnant ewes. In response to intravenous cocaine doses of 1.0 and 2.0 mg/kg, both pregnant and nonpregnant ewes demonstrated dose-dependent increases in systolic, diastolic, mean arterial, and pulse pressures with return to baseline by 30 to 60 minutes after cocaine administration. However, at both doses (1.0 and 2.0 mg/kg) pregnant ewes demonstrated greater increases in mean arterial pressure (+29.6%, +48.7%) than nonpregnant ewes (+15.6%, +27.7%) during the first 5 minutes after cocaine administration. Thereafter the responses were similar. Thus pregnancy increases the cardiovascular toxicity to cocaine.