158 school children from Lambarene and its surroundings suffering from intestinal manifestations of schistosomiasis due to Schistosoma intercalatum, Schistosoma haematobium, or mixed infections were randomly allocated to patient groups to be treated with oltipraz and praziquantel respectively. Oltipraz was tested in three dosage regimens, i.e., 1 X 25 mg/kg, 1 X 35 mg/kg, and 2 X 20 mg/kg and compared to 2 X 30 mg/kg praziquantel in each of the treatment groups. 45 days and 90 days after treatment, the children were thoroughly investigated. Rectoscopy was only performed in part of the children. The number of children with viable egg excretion had significantly dropped after therapy (p less than 0.001). Parasitological cure after 90 days was obtained in 86% of patients treated with 2 X 20 mg oltipraz and 90% of patients treated by praziquantel. A comparative effectiveness was achieved with the other dosage regimens of oltipraz, too. The efficacy of the new schistosomicid oltipraz is identical with that of praziquantel for patients with intestinal manifestation. The rectal biopsies taken 45 days and 90 days after therapy still contained numerous eggs which were mostly calcified or granulated.