Alpha-I-antitrypsin immunoreactivity was demonstrated by immunofluorescence in epithelial cells of the normal human small intestine. Its presence was also confirmed in biopsies of patients with Crohn's disease. Specific fluorescence was observed in only four out of 14 adult patients with coeliac disease. These results implicate the human small intestinal epithelium as a possible source of alpha-I-antitrypsin. The absence of positive cells may have implications in the aetiology of coeliac disease.