Diarrhea is a common event in the clinical history of cancer patients. It can be caused by the presence of tumor or it can be a side effect of treatment. The latter problem is occurring more often because new drugs (CPT-11) or drug combinations (fluorouracil plus interferon or leucovorin) have diarrhea as the dose-limiting toxicity. The clinical use of octreotide, a long-acting somatostatin analogue, seemed to demonstrate an improvement in most diarrheal states induced by tumors (endocrine tumors) or by treatments (short bowel syndrome; chemotherapy-induced diarrhea).