A series of 3-alkyl(aryl)-4-(p-hydroxy -phenyl)-4,5-dihydro-1H-1,2,4-triazol-5-ones 2 were obtained from the reaction of alkyl (aryl) ester ethoxycarbonyl hydrazones I with p-hydroxy aniline. The reaction of I with 1,4-diamino benzene (1:1) to afford 3-alkyl(aryl)-4- (p-aminophenyl)-4,5-dihydro-1H-1,2,4-triazol-5-ones 3. The reaction of 3 with benzaldehyde gave 3-alkyl(aryl)-4-(4'-benzilidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones 4. All of the above reactions occurred under microwave heating and conventional methods. Their structures were confirmed by H-1 NMR, C-13 NMR, IR, and elemental analyses. (C) 2008 Wiley Periodicals, Inc.