Disclosed are 1,2-benzisoxazole and 1,2-benzisothiazole derivatives represented by formula I ##STR1## wherein X represents oxygen or sulfur; Z rep;esents carbon (CH) so as to complete the imidazol-1-yl ring radical or Z represents nitrogen (N) so as to complete the 1,2,4-triazol-1-yl ring radical; R.sub.1 represents hydrogen, lower alkenyl, lower alkynyl, aryl-lower alkyl or lower alkyl; R.sub.2 represents hydrogen, lower alkenyl, lower alkynyl, aryl-lower alkyl or lower alkyl; or R.sub.1 and R.sub.2 combined represent lower alkylene; or R.sub.1 combined with R.sub.5 located on the Z-carbon atom of the imidazolyl radical represents C.sub.2 -C.sub.4 -alkylene; R.sub.3 and R.sub.4 independently represent hydrogen, lower alkyl, cycloalkyl, halogen, trifluoromethyl, cyano, nitro, amino, hydroxy, lower alkanoyloxy, carbocyclic aroyloxy, lower alkoxy, or carbocyclic aryl; or R.sub.3 and R.sub.4, together when located on adjacent carbon atoms, represent lower alkylenedioxy; or R.sub.3 and R.sub.4, together when located on the carbon atoms to which attached a benzo-fused or C.sub.5 -C.sub.7 -cycloalka-fused ring, respectively; R.sub.5 located on carbon represents hydrogen, lower alkyl or hydroxy-lower alkyl; R.sub.6 located on carbon represents hydrogen or lower alkyl; or when Z represents carbon, R.sub.5 located on the Z-carbon atom combined with R.sub.6 located on the adjacent carbon atom represents C.sub.3 -C.sub.5 -alkylene; and pharmaceutically acceptable salts thereof; which are active in mammals as anticonvulsant agents.