Anti-reticulin antibodies were measured by an indirect immunofluorescence method in 195 consecutive patients with insulin-dependent diabetes mellitus, and positive titres were found in 8 patients. A jejunal biopsy was performed in these patients, all of whom had small-intestinal atrophy. Thus the frequency of coeliac disease in adult diabetes patients was 4.1%. The patients had no signs of malabsorption or of significant abdominal complaints. We conclude that coeliac disease is commoner in type-I diabetes than in the normal population, and measurement of anti-reticulin antibodies seems to be a suitable screening method.