In order to investigate effects of khat chewing on uteroplacental blood flow, eight awake, chronically catheterized guinea pigs were fed 2.2 g khat leaves/kg in late pregnancy and regional blood flows were measured with the microsphere technique. Seven animals fed with aspen leaves in the same amounts served as controls. The mean concentration of (+)-norpseudoephedrine in urine 3 h after the end of the feeding was 4.6 micrograms/ml in the khat-fed group with no detectable amounts in the controls. Placental blood flow was reduced by 10% 75 min and by 24% 180 min after khat feeding. Since the khat dose used gave urinary concentrations of (+)-norpseudoephedrine of the same magnitude as those reported in khat chewing women, khat chewing in pregnancy may reduce placental blood flow and impair fetal growth.