The calcium antagonistic and alpha 1-adrenergic receptor blocking activities of monatepil maleate (CAS 103377-41-9, (+/-)-N-(6,11-dihydrodibenzo [b, e] thiepin-11-yl) -4-(4-fluorophenyl)-1-piperazinebutanamide monomaleate, AJ-2615), a novel calcium antagonist, its metabolites and their enantiomers were studied in vitro. Monatepil maleate inhibited calcium-induced contractions of rat thoracic aorta (pA2 = 8.71) and l-phenylephrine-induced contractions of rabbit superior mesenteric artery (IC50 = 56.6 nmol/l). The calcium antagonistic activities of the metabolites of monatepil maleate (AJ-2615-sulfoxide A, AJ-2615-sulfoxide B and AJ-2615-sulfone) were 1/10 of that of monatepil maleate. However, their alpha 1-adrenergic receptor blocking activities were similar to or slightly more potent than that of monatepil maleate. The potencies of the calcium antagonistic activities of monatepil maleate and its enantiomers [(S)-AJ-2615 and (R)-AJ-2615] were in the order of (S)-AJ-2615 > monatepil maleate > (R)-AJ-2615 whereas no difference was observed among them in alpha 1-adrenergic receptor blocking activity. In calcium antagonistic and alpha 1-adrenergic receptor blocking activities, there was no difference between the enantiomers of monatepil maleate metabolites. In conclusion, there was a difference with several times in calcium antagonistic activity between the two enantiomers of monatepil maleate but not in their alpha 1-adrenergic receptor blocking activity.