The biopsy specimens and sera from 269 adult patients referred for gastroscopy were examined for Helicobacter pylori infections. The bacteriologic studies included: Gram smears, urease test and culture methods of biopsy specimens, biochemical tests for identification of isolates and their sensitivity testing to 17 chemotherapeutics. The biopsy specimens were examined histopathologically also. For demonstration of specific antibodies the latex test (Pyloriset, Orion Diagnostica, Finland) was used. Biopsy--cultures were positive for H. pylori in 171 (63.6%) cases, biopsy--urease test in 149 (55.4%) and Gram smears in 163 (62.8%). A total of 193 (71.7%) positive sera with latex were found. The sensitivity and specificity of the latex test as compared with the culture method, biopsy--urease test and Gram smears was 80.7% and 43.9%, 80.5% and 39.2% or 79.8% and 40.6% respectively. All three direct diagnostic methods were positive in 122 (45.4%) patients, 101 (82.8%) of them were positive with the latex test. Only in 33 (19.3%) patients with positive biopsy--culture for H. pylori anti-H. pylori antibodies were not observed. On the other hand, among 75 patients with negative all direct methods for H. pylori infections 39 (52.0%) of them were positive with the latex test. The latex test was also positive in 56 (54.9%) sera among 102 blood donor tested by us but this value was lower, in trems of statistical significance than in patient sera. In conclusion, the latex test may be useful as a screening serological test for the diagnosis of patients with H. pylori infections and for epidemiological studies.