To evaluate the possible contribution of enteric losses of alpha 1-antitrypsin (alpha 1-AT) to the low serum levels of alpha 1-AT seen in patients with alpha 1-AT deficiency, we investigated intestinal clearance of alpha 1-AT (C-alpha 1-AT) in five of these patients (mean age 3.4 years) and compared it to that of 10 patients (mean age 3.7 years) with gastrointestinal disorders and normal serum albumin values who served as controls. C-alpha 1-AT was also determined in four patients (mean age 9 months) with noncirrhotic liver disease. The percent of daily alpha 1-AT turnover which could be attributed to stool losses was calculated in these groups of patients. alpha 1-AT was measured in stool and serum by radial immunodiffusion and the clearance calculated. The mean C-alpha 1-AT in the patients with alpha 1-AT deficiency was significantly (p less than 0.05) higher than that of the controls. The liver disease patients had values for C-alpha 1-AT in the range of the controls. Three of the alpha 1-AT deficiency patients had values for C-alpha 1-AT greater than the mean plus 3 SD of the control, but these were not in the range seen in patients with protein losing enteropathy. Mean percent contribution of stool losses to total daily alpha 1-AT turnover was similar in all three groups. We conclude that patients with alpha 1-AT deficiency have increased fecal clearance of alpha 1-AT seemingly unrelated to the liver disease, but that this is not a major cause of the low serum levels.