We studied maternal and fetal blood pressure, heart rate, arterial blood gases and fetal behavioral state alterations in response to maternally administered cocaine hydrochloride in 11 pregnant sheep. Cocaine administration to the ewe caused a dose-dependent increase in maternal blood pressure and heart rate and in fetal blood pressure, and a decrease in fetal arterial oxygen tension. In the ewe, blood pressure changes corresponded linearly to dose administered (r = 0.88, p less than 0.001). Blood pressure changes were correlated to peak plasma cocaine concentration in the ewe (r = 0.52, p less than 0.01) and in the fetus (r = 0.43, p = 0.05). In addition, in 7 of 8 fetuses which had entered rapid eye movement (REM) sleep within 5 min of maternal cocaine administration, REM sleep was abruptly terminated either by the cocaine, fetal hypoxia or some other nonspecific event caused by the maternal cocaine administration. Maternal cocaine administration causes maternal and fetal hemodynamic alterations that have potential adverse effects in pregnancy.