An ELISA for detection of IgG, IgA, and IgM antibody using an acid-glycine extract from Campylobacter jejuni as antigen was developed. To determine the value of this assay for the diagnosis of acute Campylobacter jejuni infections, the IgG, IgA, and IgM immune response against Campylobacter jejuni was investigated at various timepoints after infection in patients with culture-proven infection. A total of 112 sera from 46 patients and 78 sera from a control group were tested. All but one of the 46 patients with culture-proven Campylobacter jejuni enteritis developed IgG antibodies against Campylobacter jejuni. IgA and IgM ELISA both showed 97% specificity, and sensitivity of 63% and 30% respectively. IgG antibody titers generally remained at a constant level for more than 50 days, whereas IgA and IgM antibody titers declined more rapidly to normal values within 30 to 50 days after onset of clinical symptoms. Detection of Campylobacter jejuni specific IgA antibodies in a single serum sample provided the most useful assay for serological diagnosis of Campylobacter jejuni enteritis. The presence of Campylobacter jejuni specific IgM antibodies was the sole diagnostic criterion in three cases. Serological diagnosis of Campylobacter jejuni enteritis should therefore include both IgA and IgM antibody determination.