A series of 3-alkyl-4- (arylidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones, 6-10, was obtained from the reaction of the corresponding 3-alkyl-4-amino-4,5-dihydro-1H- 1,2,4-triazol-5-ones, 1, with the appropriate aldehydes. 3-alkyl-4-(alkylamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones of type 11-16 were synthesized from the selective reduction of compounds 5-10 with NaBH4 in diglyme or DMSO medium as a general and convenient method.