A monoclonal antibody was developed for detection of Helicobacter pylori in gastric tissue sections in a direct immunofluorescence test. On a comparison of the immunofluorescence test with standard methods for detection of Helicobacter pylori, i.e. culture, the urease activity test and histological examination of tissue sections, using 158 biopsy specimens, 30 specimens were positive in all methods and 64 negative. In the remaining cases comparison was not possible because either immunofluorescence (29 specimens) or the standard methods (16 specimens) gave ambiguous results. The direct immunofluorescence test may have potential as an alternative to standard methods, but further testing in a defined patient population is necessary.