Abstract: The schistosomicidal effect of F30385 on larval stages is much stronger than that on adult forms in experimentally infected mice, rabbits, and dogs. With a course of treatment of 100 mg/kg/day×2 in rabbits and 50 mg/kg/day×2 in dogs commenced 7 or 14 days after exposure to cercariae, a vermicidal effect of 85～100% was obtained. Three of the six dogs were free from infection. In comparison with F30066 at the dosage of equal toxicity, the vermicidal effect of F30385 on schistosomula in mice and rabbits were stronger than that of F30066. In order to avoid or reduce the incidence of acute schistosomiasis, it is proposed that a 2-day protective treatment with F30385 every 14 days during the period of contact with infective water is worthy of study.