A surface antigen (SA), acid glycine extract (AGE), and urease preparation (UP) were evaluated using sera from patients undergoing endoscopy and from subjects with gastric or duodenal ulcers. Sera were tested for the presence of IgG and IgA antibodies by a conventional indirect enzyme linked immunosorbent assay (ELISA). In patients with confirmed Campylobacter pylori associated gastritis, raised IgG antibody titres were indicated by absorbance values of greater than or equal to 500, greater than or equal to 500, and greater than or equal to 1500 for the SA, AGE, and UP, respectively. Corresponding values for the IgA assay were greater than or equal to 500, greater than or equal to 500, and greater than or equal to 1000. The specificity of the IgG assays were 94%, 92%, and 90% for the AGE, SA, and UP, respectively. In contrast, the UP was the most sensitive (97%); the other two antigen preparations gave values of 82%. In the IgA assay the UP showed the greatest specificity (90%) and sensitivity (90%). The predictive value for a true positive for the IgG assay was the same for all antigens (93%), whereas the UP gave a predictive value for a true negative of 96% compared with 79% for the other two antigen preparations. Of the patients with gastric or duodenal ulcers, raised antibody titres to SA were found in 72% (IgG) and 73% (IgA), to AGE in 75% (IgG) and 63% (IgA), and to UP in 77% (IgG) and 75% (IgA). The use of a urease antigen preparation to determine IgG antibody is recommended for screening patients undergoing endoscopy.