The reliability of random fecal alpha 1-antitrypsin (FA-1-AT) concentration has been evaluated by comparing FA-1-AT values on random specimens and on concomitant 24-72 h fecal collections. In order to simplify the method, FA-1-AT data derived from lyophilized fecal samples were compared with those obtained from 37 degrees C heat-dried fecal samples. Random FA-1-AT concentration was assayed in 80 children with various gastrointestinal illnesses and 36 healthy age-matched controls. There was a close relationship between FA-1-AT values obtained from random samples and 1-day or 3-day collections. There was also a significant relationship between FA-1-AT values derived from the two different ways of drying the stools. Mean FA-1-AT values were statistically different when compared to the controls in the following groups of disorders: untreated and after-gluten-challenge celiac disease, post-enteritis syndrome, and cow's milk intolerance. The possible meanings of the abnormal FA-1-AT concentration in the various disorders are discussed. We conclude that FA-1-AT is a simple and reliable test for enteric protein loss. The simplification of the method proposed by us should reduce the cost of the test and moreover make it feasible in all laboratories.