The effects of nicardipine, a calcium-entry blocker which also has a potent phosphodiesterase inhibitory action, were investigated on isolated human term-pregnant and nonpregnant myometrium, and compared with those of nifedipine. Both drugs relaxed pregnant and nonpregnant myometrial preparations contracted by potassium (127 mM), and also reduced or abolished contractions occurring spontaneously, or induced by pros-taglandin F2α, oxytocin and vasopressin. However, the effect of nicardipine had a slower onset of action than that of nifedipine, and the drug was significantly more potent than nifedipine in pregnant but not in nonpregnant myometrium. It is concluded that in vitro nicardipine is at least as effective as nifedipine. If the differences between the drugs can be reproduced also in vivo, nicardipine offers an interesting alternative to nifedipine for inhibition of undesired uterine activity.