The effects of pulmonary artery infusion of delta-9-tetrahydrocannabinol (delta 9-THC), 0.5 mg/kg, have been studied in four pregnant sheep. Cardiac output (CO) decreased from a baseline of 4.49 +/- 0.91 l/min (mean +/- s.e.m.) to 4.19 +/- 0.87 at 3 min, 3.69 +/- 0.76 at 5 min, and 3.35 +/- 0.77 at 15 min post infusion and returned to baseline by 1 h post infusion. Maternal blood pressure (MBP) decreased from 114 +/- 9 to a nadir of 69 +/- 8 mmHg at 15 min post infusion. Uterine artery blood flow (UTABF) increased from 256 +/- 88 to 317 +/- 132 ml/min at 3 min post infusion, but this was not statistically significant. Maternal acidosis, hypercapnia, and hypoxemia also developed during the first 15 min post infusion. Although fetal blood pressure (FBP) decreased throughout the 1st h post infusion, statistically significant changes in FBP or fetal heart rate (FHR) were not observed. Umbilical artery blood flow (UMABF) increased from 188 +/- 58 to 211 +/- 68 1/min at 5 min post infusion and declined thereafter. This change was also statistically significant. As in the ewe the fetus developed acidosis and hypoxemia, but hypercapnia, although present, was not statistically significant. A single animal was studied following i.v. infusion of delta 9-THC (1 mg/kg). More pronounced effects, including a decrease in UTABF and UMABF, were noted. The sheep were maintained under pentobarbital anesthesia for the duration of the study.