Starting from Miracil D (Lucanthone), a hydroxymethyl derivative (Hycanthone) can be obtained through the biological activity of the microorganism Aspergillus sclerotiorum. This compound was claimed to be the antischistosomal metabolite of Miracil D and was found very active when administered to mice, hamsters and Cebus monkeys experimentally infected with Schistosoma mansoni. Clinical trials with Hycanthone were performed on 52 patients with active schistosomiasis mansoni. The drug was administered, per os, at the dose leveis of 2 and 3 mg/kg/day with an antacid preparation, twice a day, for 5 consecutive days. In all but 2 patients treatment could be completed. Nausea and/or vomiting, anorexia, vertigo and headache were the commonest side effects. Therapeutic activity toas evaluated by repeated stool examinations (4 to 6) and one rectal biopsy performed at least 4 months after treatment. The percentages of patients considered as cured were 83.3 and 80.0 for the schedules of 2 and 3 mg/kg, respectively. Laboratory and clinical data on the antischistosomal activity of Hycanthone obtained so far emphasize need for further clinical trials with this compound.