One of the characteristic features of celiac disease is an increase in anti-gliadin antibodies (Abs). Recently we found that some of the monoclonal Abs to gliadin cross-react with molecules on rat enterocytes. One of these cross-reacting molecules was identified as rat calreticulin. This study shows that the levels of serum IgA Abs to gliadin, rat, and human enterocytes; purified enterocyte antigens; and calreticulin in sera from patients with active disease were significantly higher than in patients on a gluten-free diet and healthy controls (P < 0.001). Anti-gliadin Abs were isolated by affinity chromatography from the sera of six active celiac patients. The reactivity of these anti-gliadin Abs was demonstrated to be significantly higher (P < 0.05) with human enterocytes and human calreticulin than with other antigens tested. Furthermore, using isolated patients' anti-gliadin Abs bound to Sepharose 2B, two main proteins of molecular mass 62 and 66 kDa were purified from a lysate of human enterocytes. The 62-kDa enterocyte antigen was identified as human calreticulin. These findings suggest that anti-gliadin Abs may play a pathogenic role in celiac disease by cross-reacting with enterocytes. Calreticulin in enterocytes may be one of the putative targets for autoimmune reactions.