BACKGROUND: Inhalation anesthetics have been known as vasodilators, but there are several reports that halothane and enflurane have different effects on vascular smooth muscles. Vasodilatation and vasoconstriction were observed in different vessels in the same animal. We tried to observe the effect of halothane and enflurane on the contraction of the aorta in rabbits. METHODS: Isolated tracheal preparations of rabbits were used. Halothane (1.4%) and enflurane (1.4%, 2.8% and 5%) were administered after contractions induced by phenylephrine (10(-7) M), and verapamil (10(-7), 10(-6), 10(-5), 10(-4), and 10(-3) M) was administered. In the verapamil pretreated group, after a phenylephrine (10(-7) M) induced contraction, verapamil (10(-7) M) and enflurane (2.8% and 5%) were administered. The percentile contraction to the contraction induced by phenylephrine was evaluated. RESULTS: The potentiation of the contration by phenypephrine was observed by halothane and enflurane administration and these potentiations disappeared with the adminstration of verapamil. With prior administration of verapamil, there was no potentiation of the contraction by enflurane. CONCLUSIONS: Halothane and enflurane potentiates the contraction induced by phenylephrine in rabbit aortas. In addition, the influx of extracellular calcium seems to play a role in this potentiation of the contraction.