Sera from 1866 healthy blood donors and from 40 untreated adults with celiac disease were analyzed using a micro-ELISA assay. Blood donors with IgA antigliadin activity greater than 40 units corresponding to the 96.8th percentile and IgG antigliadin activity greater than 20 units corresponding to the 91.3rd percentile were selected for further investigation and jejunal biopsy. Seven of 49 blood donors with high IgA antigliadin activity showed mucosal lesions typical for celiac disease. None of the donors with high IgG antigliadin activity (35 subjects) but without high IgA activity had such mucosal lesions. A prevalence of celiac disease of at least 1/256 was observed in the donor group. There were significant age-group differences in IgA antigliadin activity. In the present study, a high IgA antigliadin activity had a positive predictive value between 18% and 25% in individuals without symptoms indicative of celiac disease depending on the way the cut-off points were chosen. In contrast, the positive predictive value of high IgG antigliadin activity alone was estimated to be 0%.