In order to investigate effects of khat chewing on uteroplacental blood flow (+) norpseudoephedrine (NPE) infusions were given to 11 anesthetized guinea pigs in late pregnancy (62–66 days) after unilateral uterine artery ligation at days 30–32. Regional blood flows were determined with radioactive microspheres. Mean arterial blood pressure increased with 25% and heart rate with 9% during NPE infusion. Myoendometrial blood flow was reduced by 31 %. Placental vascular resistance (PVR) increased by 56% in the control horn (17 fetuses) and by 82% in the ligated horn (17 fetuses). This vasoconstriction was counteracted by the systemic vasopressor response since placental blood flow remained unchanged. When considering only the 13 growth-retarded fetuses, however, PVR increased by 98% and a 19% reduction of placental blood flow could be demonstrated. These results suggest that the placenta of the growth-retarded fetus may be more sensitive to adrenergic stimulation than the normal placenta. Furthermore, since one of the active constituents of khat, (+)norpseudoephedrine, causes vasoconstriction in the uteroplacental vascular bed it is possible that khat chewing could reduce placental blood flow and, as a consequence, impair fetal gro