We investigated the significance of rapid turnover proteins (retinal-binding protein, pre-albumin and transferrin) in protein-losing gastroenteropathy. We evaluated the levels of these proteins in 12 patients with protein-losing gastroenteropathy. The protein-losing gastroenteropathy patients showed very low level of total serum protein of 4.3 +/- 0.7 g/dL, albumin 2.1 +/- 0.4 g/dL, and IgG 682 +/- 232 mg/dL. However, retinal-binding protein was 4.4 +/- 1.9 mg/dL (normal range; 2.5-8.0 mg/dL), pre-albumin 29.3 +/- 7.9 mg/dL (21-43 mg/dL) and transferrin 226 +/- 62 mg/dL (205-370 mg/dL). The levels of rapid turnover proteins, particularly retinal-binding protein and pre-albumin were almost preserved within the normal range, despite hypoproteinemia. If there is a patient with severe hypoproteinemia and preserved levels of rapid turnover proteins, protein-losing gastroenteropathy should be suspected and we get a strong proof to do the following examinations such as a fecal clearance of alpha-1 antitrypsin.