Abdominal scintigraphy with intravenous injection of 99mTc-labeled serum albumin was performed in 6 patients with protein-losing enteropathy (PLE) and 3 patients with non-gastrointestinal tract disorders. In 3 out of 6 patients with PLE, abnormal radioactivity was observed in the ileum region 3 hours after injection, and thereafter clear colon image was obtained. In the remaining 3 patients, the colon was visualized 24 hours after injection. On the other hand, in all patients with non-gastrointestinal tract disorders, no abnormal radioactivity was observed in the abdomen until 24 hours after injection. These results indicate that gastrointestinal protein loss could be demonstrated by scintigraphy with intravenously administered 99mTc-labeled serum albumin. In one healthy subject, 99mTc-labeled serum albumin was administered orally and abdominal scintigraphy was performed. Gastrointestinal tract image was only observed and no other image was demonstrated until 24 hours after oral administration. This result suggests that 99mTc excreted into the gastrointestinal tract is not reabsorbed. Therefore, abdominal scintigraphy with 99mTc-labeled serum albumin appears to be a simple and useful method for diagnosis of PLE.