Specimens of mucosa from the small intestine were obtained from several hundred persons by using the Crosby intestinal biopsy capsule. Normal histologic variations have been recognized. Acute diarrheal diseases, including Asiatic cholera, were found to be characterized by inflammatory changes, while specimens from patients with severe tropical or nontropical sprue showed inflammation, atrophy, and amorphous proteinaceous amphophilic precipitates in the stroma. In cases of Whipple's disease the characteristic finding was heavy infiltration of the lamina propria by macrophages which contain polysaccharide stained by para-aminosalicylic acid. There are many research applications for this technique for obtaining fresh, small samples of intestinal mucosa, unaffected by surgical trauma or postmortem autolysis. It has been particularly useful in establishing the diagnosis and evaluating the treatment in patients with intestinal "malabsorption syndrome."