With an immunological technique, presence of albumin was searched in the stools of 47 patients with cystic fibrosis and 54 controls. Albumin was found in 93% of cystic fibrosis, at a mean level of 90 mg/100 g of fresh stools. The test was negative in the 54 healthy controls. It was positive in one case of congenita IgA deficiency and in one untreated case of Hirschprung's disease. When found in the stools, albumin may give a useful additional diagnostic element.