Accurate diagnosis of Helicobacter pylori infection is very important in both clinical practice and research. We evaluated the sensitivity of real-time PCR (RT-PCR) for the detection and quantification of Helicobacter pylori using DNA from 91 human gastric biopsy samples divided into three groups: 46 biopsies from untreated patients who according to the references methods were considered H. pylori-negative (group A); 35 biopsies from patients previously treated against H. pylori and considered to be cured by "gold standard" tests (group B); and 10 biopsies from patients H. pylori-positive by all available methods (group C). The sensitivity of the RT-PCR assay was higher than that of standard methods. Of the 81 patients considered to be uninfected according to the references methods, 16 were H. pylori-positive by PCR, 10 of which were patients who had received H. pylori eradication therapy and 6 were untreated patients. Based on these findings we recommend that RT-PCR should be use in addition to standard methods in clinical studies to monitor the results of H. pylori eradication therapy.