An immunohistochemical assay for staining C. pylori is described. The method is compared with cultivation of C. pylori and observation of campylobacter-like organisms (CLOs) in hematoxyline-eosine (HE) stained sections. Eighteen biopsies from which C. pylori was cultivated but not seen in HE stained sections and three culture negative biopsies with CLOs seen in HE stained sections were selected from 331 biopsies including 113 culture positive biopsies. There were agreements between cultivation of C. pylori and CLOs seen in HE stained sections in the remaining 310 biopsies. Fourteen of the 18 and one of the three biopsies were found positive by the immunohistochemical assay. In addition 21 culture-positive control biopsies and one of 18 culture-negative control biopsies were also found positive. When the immunohistochemical assay was compared with cultivation the predictive value of positive result is 93% and of negative result 89%. By this method we were able to detect single organisms and no cross-reactions to other curved bacteria on the gastric epithelium were observed.