The development of a rapid and specific diagnostic assay for Campylobacter infections is important in determining the etiology of acute diarrhea in humans. Studies have shown that sonicated whole bacteria or partially purified antigens cross-reacted with antibodies against other closely related bacteria. To solve the problems of specificity, we identified specific antigens of Campylobacter jejuni and Campylobacter coli for use in diagnostic assays. We investigated the responses of serum, urine, and intestinal lavage antibodies in infected (fed live bacteria) and parenterally immunized (intraperitoneal injection of sonicated whole bacteria with adjuvant) mice directed against C. jejuni or C. coli by Western blot (immunoblot) analysis. Antibody responses were examined weekly for up to 28 days. Fewer antigens were detected by urinary and intestinal lavage fluid immunoglobulin A (IgA) than serum IgG and IgM for both parenterally immunized and infected mice. Serum from parenterally immunized mice detected more antigens than that from infected mice. Two high-molecular-weight antigens (62,000 and 43,000) were predominantly detected by serum, urine, and intestinal lavage fluids of both parenterally immunized and infected mice. Serum antibodies from 28-day parenterally immunized mice detected one antigen specific to C. coli with a molecular weight of 38,000 and one antigen specific to C. jejuni with a molecular weight of 27,000. An immunodominant protein with a molecular weight of 31,000 common to both C. jejuni and C. coli was also recognized by serum antibodies from parenterally immunized mice.