Fecal alpha 1-antitrypsin excretion, a noninvasive indicator of protein-losing enteropathy, was correlated with clinical disease activity in pediatric patients with Crohn's disease. Disease activity was defined as the sum of 11 abnormal clinical parameters which were adapted from previously published disease activity scoring methods. Each patient was also given a subjective clinical rating when evaluated. In addition, four different devised disease activity scoring methods were correlated retrospectively with subjective clinical ratings for hospitalized patients. A total of 125 random fecal alpha 1-antitrypsin determinations were performed on 22 patients. Ninety-six percent of clinically active episodes of Crohn's disease were associated with elevated fetal alpha 1-antitrypsin (p less than 0.001). The degree of elevation was found not to correlate directly with the severity of assessed disease activity or site of intestinal involvement. A direct linear relationship was demonstrated between 23 paired random fecal alpha 1-antitrypsin and intestinal alpha 1-antitrypsin clearance assays (r = 0.93). There was a high, and remarkably similar, degree of correlation with each of the four different derived activity scoring methods and simple subjective ratings (r = 0.89-0.93). We conclude that: (a) fecal alpha 1-antitrypsin excretion may be helpful in assessing the presence or absence of Crohn's disease activity by providing an objective and specific indicator of intestinal damage; and (b) it appears that a simple subjective rating score is as clinically useful as other previously devised activity indices.