Abstract: Twenty-eight new derivatives of 4-phenyl-and 4-allyl-5-(pyrazinyl2)-l,2,4-triazole-3-thio-ketone (II and III) were synthesized. The key intermediates 4-phenyl- and 4-allyl-substituted l-(pyrazinyl-2) formyl-thiosemicarbazide were obtained from ethyl-(pyrazinyl-2)-carboxylate by hydrazinolysis and reaction subsequently with phenyl or allyl isothiocyanate. They were cyclized in the presence of 2N sodium hydroxide to form II and III, followed by alkylation, acylation and Mannicb reaction under various suitable conditions to afford the corresponding compounds. After preliminary screening two compounds (III₁, III₂) were found to have pro nounced effect on liver shift of Schistosoma japonica in experimental mice.