A Tanzanian man with a known seizure disorder was admitted to hospital for treatment of schistosomiasis mansoni. He suffered a grand mal seizure soon after the second dose of oxamniquine. This is the first recorded seizure associated with use of this drug. Two other cases are reported in which transient electroencephalograph changes occurred during oxamniqueine therapy. The central nervous system effects of oxamniquine are reviewed with respect to its possible epileptogenic effects.