The effects of verapamil on acetylcholine and field stimulation induced contraction were studied in the isolated ileum of newborn, 5, 10, 15, 20 and 30 day old guinea-pigs. Verapamil inhibits the contraction evoked by acetylcholine or by field stimulation, being more affected the response to acetylcholine than to field stimulation. Verapamil IC50's against acetylcholine and field stimulation differ throughout the periods of development considered. These data suggest that the function of verapamil-sensitive calcium channels of guinea-pig ileum involved in the response to acetylcholine and field stimulation change during the period of development studied.