The authors report hier experiment with Hycanthone in a thousand patients suffering from schistosomiaasti mansoni, who have been treated in the Clinical Hospital of Guanabara University so far. The patients come from the endemical areas of the country, specially from northeast and southeast, being 53,9% males and 46,1% females, aged between 5 and 63. The prevailing clinicai form of the parasitosis was the hepatic-intestinal (96,%). The medicine has been applied in a single dosage, at the rate of 3 mg/kg of body weight, 33 6% in in-patients and 66,4% at the stage of ambulatorial treatment. The serum leveis of the transaminases determined for comparison before and after the use the produet, in 60 of the in-patients, did not modify, or just suffered inexpressive raising. There were no side-effects in 42,3% of the patients. In . the others, thore effects were of little and medium intemily and lasted only the first day in most cases, and consisted specially of nauseas and vomits. The parasitical cure control was performed through 4 stool examinations, at the end of 30, 60, 90 and 120 days of the medicine employment, and it has been done in 330 patients (33%), with 99% of cure. By including the rectal biopsy whenever, it was possible, by the time of the 4th stool examination, the procedure had worked out well with 97 patiens (9,7%), and among them 92 (94%), are now cured, according to that criter on. This paper confirms the schistosomicidal activity of the Hycanthone, as well as its good tolerance, including regarding the hepatic cells. The patients, however, must be carefully selected, taking into account the known counter-indications, mainly concerning the liver.