Bupivacaine is a commonly used local anesthetic in obstetrical practice, but since this compound also has a constrictor action on vascular smooth muscle it can be hazardous to the fetus. The aim of the present study was to analyze the effect of bupivacaine on the uterine vasculature using the rat uterine artery as a model. Small arterial segments were mounted in tissue chambers for isometric recording of vascular tension using a specially designed teflon-steel gauge. Bupivacaine induced marked vasoconstriction and this vasoconstriction was reduced considerably by two different Ca antagonists, verapamil and nifedipine. Verapamil (10(-5) mol.l-1) reduced bupivacaine-produced arterial contraction by a mean of 78% and nifedipine (2.9 x 10(-7) mol.l-1) reduced arterial contraction by a mean of 57%.