Clinicians have multiple tests at their disposal when evalu-ating a patient with chronic diarrhea, and proper judgment should be used in choosing the most appropriate ones. Duration of diarrhea, evidence of systemic involvement, nutritional de-ficiencies and previous investigations should guide the evalua-tion of the patient. In contrast to acute diarrhea, infectious etiology is uncommon with chronic diarrhea. Weight loss and evidence of nutritional deficiencies suggest malabsorption caused by a pathologic process in the small bowel or pancreas, the latter implicated by a history of excessive alcohol intake or abdominal pain. Chronic bloody diarrhea suggests inflammato-ry bowel disease, particularly ulcerative colitis. Chronic diar-rhea with no evidence of nutritional or metabolic deficiency suggests lactose intolerance (common); irritable bowel syn-drome, particularly when associated with abdominal pain (common); microscopic colitis (particularly in elderly wom-en); fecal incontinence; or surreptitious laxative abuse. Colon cancer should always be ruled out. Large-volume diarrhea, in the absence of nutritional deficiencies, with features of a secre-tory process usually prompts a search for hormone-producing tumors, but they are rarely found. Therapy is directed toward the underlying etiology when possible. When no specific thera-py is available (as in microscopic colitis) or no cause is found,it is appropriate to give empirical therapy (such as antibiotics for possible bacterial overgrowth or Giardia infection, or cholestyramine for bile acid malabsorption) or nonspecific ther-apy with constipating agents such as loperamide, diphenoxy-late, and, in more severe cases, codeine, paregoric, or a trial of long-acting somatostatin analogue. A general algorithm for the approach to chronic diarrhea is illustrated in Figure 2.

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