The inhibitory effect of nisoldipine (Baymycard, Syscor; CAS 63675-72-9) and nifedipine on the serotonin and potassium induced contractions of porcine coronary and femoral arteries in vitro has been investigated. Both nisoldipine and nifedipine inhibited preferentially the serotonin induced contraction in the coronary artery being less effective in the inhibition of the femoral artery. The coronary selectivity of nisoldipine is at least 10 times more pronounced than that of nifedipine. The serotonin antagonist ketanserin inhibited contractions on both vessels with the same potency. The potassium induced contraction was inhibited by the dihydropyridines in both coronary and femoral artery. Nisoldipine again, was more potent than nifedipine in the inhibition of coronary artery spasm but not in the contraction of femoral artery. Ketanserin did not inhibit contractions of any vessels.