Abstract: A new antischistosomal agent (S72014), 1-(5-nitro-2-thiazolyl)-3-diisobutylami—nomethyl-2-imidazolidinone, and its homologs were synthesized by using niridazole as. starting material and appropriate secondary amines through Mannich reaction. S72014. was shown to possess pronounced antischistosomal activity in animals (mice, rabbits, dogs and monkeys) infected with Schistosoma japonicum. S72014 was 10 times less toxic than niridazole and had a chemotherapeutic index 3.5 times as great. Comparative combination tests of S72014 and niridazole with chemical convulsants in mice showed that S72014 did not produce seizure at a dose as high as ten times that of niridazole which would cause epileptic convulsion significantly. Structure-activity relationship was discussed.