Abstract: A retrospective survey on side-effects for pyquiton was made among 25,693 cases of schistosomiasis japonica treated in Jiangsu, Zhejiang, Anhui, Jiangxi Provinces and Shanghai Municipality. Teams were sent separately to the fields for on-the-spot investigation which included briefings and meetings with local medical workers responsible for pyquiton treatment, reviewing of case records, visiting to the patients when necessary and filling of a unified survey questionnaire prepared beforehand.Apart from 500 acute cases, 1,175 advanced cases and 10 cases of cerebral schistosomiasis, the majority were chronic cases. The main dose-schedule used was the 2-day pyquiton regime with a total dose of 60mg/kg (70mg/kg for children).It was supported by findings during the field survey, and agreed upon unanimously by all medical workers that pyquiton was definitely the drug of the first choice in treating schistosomiasis on account of its high efficacy and low toxicity. However, some comparatively serious side-effects did happen though with very low incidence, which included syncope (14 cases), psychotic disorder (5), relapse of schizophrenia (6), hysteria (3), epileptic s izures (8), flaccid paralysis in lower limbs (2), ataxia (1), frequent premature beats (22), auricular fibrillation (3), heart rate below 50 per minute (4), supraventricular paroxysmal tachycardia (2), first degree atrioventricular block (5), attacks of angina pectoris (1), jaundice (2), hepatic coma in advanced cases with ascites (2), serious skin rashes (18) and some delayed reactions (29). However, most of the side-effects were transient and reversible and no fatality was directly associated with the drug.