Compounds having the formula (I): ##STR00001## wherein R.sup.1 is hydrogen, lower alkyl, lower alkenyl, lower or higher alkynyl, cyclo(lower)alkyl, cyclo(higher)alkyl, cyclo(lower)alkyl(lower)alkyl, cyclo(higher)alkyl(lower)alkyl, cyclo(lower)alkenyl(lower)alkyl, aryl-fused cyclo(lower)alkyl, lower alkoxy, acyl, aryl, ar(lower)alkoxy, ar(lower)alkyl, heteroar(lower)alkyl, amino, heteroaryl, heterocyclyl or heterocyclyl(lower)alkyl, which may be substituted with one or more suitable substituent(s), R.sup.2 is hydrogen or lower alkyl, X is pyrrolidinylene or piperidinylene, Y is pyridylene, which may be substituted with one or more suitable substituent(s), Z is lower alkenylene, which may be substituted with lower alkyl or halogen, and salts thereof are useful as a histone deacetylase inhibitors.