63 patients (23--78 years) with irradiation-induced diarrhoea, the majority of them resistant to treatment with diphenoxylate, were started on 4-(p-chlorophenyl)-4-hydroxy-N,N'-dimethyl-alpha,alpha-diphenyl-1-piperidine butyramide (loperidine, Imodium) 4 mg daily. Doses were further adapted individually and the trial lasted for 3--72 days. Daily frequency and consistency of stools improved significantly, and abdominal cramps were clearly reduced. Stools became normal in 41 patients after a median time of 16.5 days (median daily dose: 4 mg), they improved in six other patients, but remained unchanged in eight and deteriorated in one patient. The remaining seven cases were not evaluated. No side-effects could be attributed to the drug.