At the rotine conditions of the Section of Parasitosis of Belo Horizonte's City Hall, ambulatóriaI employment of hycanthone was evaluated concerning its viability and side effects in patients with chronic schistosomiasis mansoni. The patients received 2.5 mg/k of hycanthone, after clinicai examination and, when necessary, laboratory tests and cardiological avaliation. Ambulatorial treatment of patients with serious hepato-splenic forms and those with other counter-indication to the use of hycanthone was ruled out. On these conditions, more than 12,000 patients were treated; no serious side reactions were observed from the inauguration of the Service up to 1974, July, which confirm the simplicity and the low risk of the scheme. The side effects observed among 790 patients acompaigned during 3 days after the treatment, were chiefíy nausea (30.1%), vomiting (24.8%) and dizziness (19.5%), while 37.7% of the reported no side reactions. Myand large the related reactions were limited to the first 24 hours after the treatment, generally regressing spontaneously. Their intensity was generally mild or moderate. Statistical tests did not demonstrate significative differences between the collateral reactions of hepato-splenic and hepato-intestinal forms of the disease, possibly because of the sample conditions. Female showed a greater number of side effects than the mate, one above the age of 15 years. Considering the patienfs age groups, vomiting was more freqent up to 15 years old, while dizziness and anorexia were predominant above this age.