or hepatic disease were compared. The reference range was derived from measurements in 20 controls without gastrointestinal disease. Alpha-l-antitrypsin excretion was increased in patients with excessive 5"Cr-albumin loss, and correlations were found between a-1-antitrypsin clearance and 51Cr-albumin excretion. Because of the considerable overlap of faecal a-l-antitrypsin excretion between controls and patients, sensitivity and specificity of the test were only 58% and 80%, respectively. This poor reliability could not be explained by sampling error or temporal variations in a-l-antitrypsin excretion. These results show that although faecal a-l-antitrypsin excretion correlates with 5"Cr-albumin excretion when whole groups of patients are studied, its poor sensitivity makes it an unreliable measure of enteric protein loss.