AIM: To understand the effect of inhibiting worm ovulation on the detection of circulating membrane antigen in Schistosoma japonicum infected rabbits. METHODS: Fifteen New Zealand rabbits were each infected with 250 S. japonicum cercariae per cuttem and a chemical, allyl thiourea, which inhibit egg formation was administrated per os at days 19 and 46 after infection. Sera were collected from rabbits before and weekly after infection and subjected to dot-ELISA for circulating antigen detection. RESULTS: Group 1 rabbits were administered allyl thiourea 295- 590 mg/d 19d post infection (p. i.) on 3 consecutive days per wk until 8 wk p. i., no circulating membrane antigen could be detected in the blood stream throuhgout the experiment. Group 2 rabbits received the same dose of allyl thiourea as that in group 1 starting from d46 p. i.. Dot-ELISA positive reaction was obtained 6 wk p. i. and lasted for 2 wk. In Group 3 untreated infected rabbits, dot-ELISA positive reaction was also detected at 6 wk p. i. and lasted for 2 wk. CONCLUSION: The positive circulating membrane antigen reaction is closely related to egg laying by the female worms.