The somatostatin analogue SMS 201-995 has been reported to be effective in treating adult secretory diarrhea due to vasoactive intestinal polypeptidoma. We report the effectiveness of this drug in treating severe refractory secretory diarrhea of uncertain etiology in an infant. The patient developed diarrhea within the first few days of life, with mean stool output of 250 ml/kg.day (expected 10 ml/kg.day). Small bowel biopsy showed mild focal enteritis. Serum levels of known gastrointestinal secretagogues were normal. No tumor was detected. Diarrhea was not adequately controlled by various drug treatments. Addition of subcutaneous SMS 201-995 produced a significant sustained decrease in stool output to 80-100 ml/kg.day. During SMS 201-995 treatment, no metabolic, hormonal, or growth abnormalities were noted. SMS 201-995 was discontinued after 9 mo because of patient irritability. Stool output rose immediately to 173 ml/kg.day, and remained stable for 6 mo. It is concluded that SMS 201-995 was a safe and effective treatment in this single childhood case of severe idiopathic secretory diarrhea.