An enzyme-linked immunosorbent assay (ELISA) employing an acid-glycine extract was used to detect IgG and IgA antibodies to Campylobacter pylori in sera from 179 patients with upper gastrointestinal disease, 174 blood donors and 65 children. The incidence of positive ELISA results clearly increased with the severity of histopathologic findings in the antrum mucosa and was also high in patients with peptic ulcers and gastric cancer. The incidence in blood donors and children was much lower and increased with age. The results achieved with the ELISA were similar to those observed previously using the immunoblot method. Differences between whole cell preparation and acid-glycine extract with respect to their protein profiles and immunoblot reactivities were minor. IgM titres were very low and could not be related to histopathological findings, peptic lesions or culture findings. The ELISA may be particularly useful for monitoring the outcome of therapy aimed at eradication of Campylobacter pylori.