Secretory immunoglobulin A (sIgA) response at the intestinal mucosa is a primary defense against enteric infections. We sought to determine which antigens of Campylobacter jejuni outer membranes elicited sIgA responses in 8 patients with naturally acquired Campylobacter enteritis using Western blot analysis of fecal extracts. Naturally acquired Campylobacter infection elicited an sIgA response in 7 of 8 patients. Of these 7 patients, 5 had Campylobacter-specific sIgA titers of 1:16 and two had titers of 1:64. The C. jejuni antigens eliciting sIgA production varied, but 5 of 8 patients exhibited reactions to a 63-kilodalton flagellar antigen, and 7 of 8 patients had a reaction with a 58- and a 44-kilodalton antigen of C. jejuni and Campylobacter coli. Reaction with a 14.5- and a 97-kilodalton antigen was observed with the only stool that contained gross blood and mucus. Reactions with Campylobacter antigens were not detected in the fecal extracts of 5 healthy individuals. Identification of the antigens of C. jejuni that elicit an sIgA response may help us to better understand the immunology of Campylobacter enteritis and to identify antigens that are important in vaccine development.