An acid glycine extract from a single Campylobacter jejuni strain was used as the antigen in the enzyme immunoassay (EIA). Elevated values indicating the presence of specific IgM and/or IgG antibodies were found in 73% of 52 patients hospitalized for campylobacter infection. A further 6% of the patients who had lower EIA values in paired serum samples showed at least a 20% change in EIA values. The same sera had been studied earlier for agglutinating antibodies using four reference campylobacter strains. 74% of the patients had shown elevated titres and a further 17% four-fold changes of lower titres in paired sera.