Gastric and fecal clearance of alpha 1-antitrypsin were measured in three cases of protein-losing gastroenteropathy and in two control cases. Abdominal scintigraphy using 99mTc-labeled human serum albumin was performed in all five subjects. All three cases of protein-losing gastroenteropathy showed 99mTc activity in the gastrointestinal tract. In the patient with hypertrophic gastropathy, the activity was seen initially in the stomach and duodenum. In the patients with intestinal lymphangiectasia, the activities were initially in the small bowel. We conclude that 99mTc scintigraphy was useful, not only in diagnosing protein-losing enteropathy, but, also, in detecting the responsible region of the gastrointestinal tract.