A compound of the formula (I): ##STR00001## (wherein Ar.sup.1 and Ar.sup.2 are independently aryl or heteroaryl, any of which is optionally substituted by a substituent selected from the group consisting of cyano, halogen, nitro, lower alkyl, halo-lower alkyl, hydroxy-lower alkyl, cyclo-lower alkyl, cyclo(lower alkyl)-lower alkyl, lower alkenyl, lower alkylamino, di-lower alkylamino, lower alkanoylamino, lower alkylsulfonylamino, arylsulfonylamino, hydroxy, lower alkoxy, halo-lower alkoxy, aryloxy, heteroaryloxy, lower alkylthio, carboxyl, formyl, lower alkanoyl, lower alkoxycarbonyl, carbamoyl, lower alkylcarbamoyl, di-lower alkylcarbamoyl, lower alkylsulfonyl, arylsulfonyl, aryl and heteroaryl; R.sup.1 and R.sup.2 are independently lower alkyl, cyclo-lower alkyl, cyclo(lower alkyl)-lower alkyl or lower alkoxy, any of which is optionally substituted by a substituent selected from the group consisting of halogen, lower alkylamino, di-lower alkylamino, lower alkanoylamino, hydroxy, lower alkoxy, formyl, lower alkoxycarbonyl, lower alkylcarbamoyl and di-lower alkylcarbamoyl; R.sup.3, R.sup.4 and R.sup.5 are independently hydrogen, cyano, halogen or hydroxy, or lower alkyl, lower alkoxy or lower alkylthio, the last three groups being optionally substituted by a substituent selected from the group consisting of halogen, lower alkylamino, di-lower alkylamino, lower alkanoylamino, hydroxy, lower alkoxy, formyl, lower alkoxycarbonyl, lower alkylcarbamoyl and di-lower alkylcarbamoyl), or a salt or ester thereof is useful as a neuropeptide Y receptor antagonist agent and is also useful as an agent for the treatment of bulimia, obesity or diabetes.