Various clinical studies indicated a lower prevalence of HP infection in HIV patients. The present study was initiated to determine whether the decreased frequency of HP infections in HIV patients might be associated with the stage of the underlying HIV disease or concomitant drug regimens the patients had received. 60 randomly selected HIV outpatients were stratified according to the stage of their HIV infection (CDC classification), their CD4 cell count and to the drug regimens they were given. Within these subgroups of patients, HP infection prevalence was separately investigated by serological and C13 breath testing. Data were compared to a reference population of 30 healthy volunteers. No difference in HP infection prevalence was found between the HIV infected patients in general and the reference cohort. A significantly lower proportion of HP infected individuals was observed among those HIV patients who had AIDS-defining diseases. Furthermore, a substantial but insignificant decrease of HP infection prevalence was noted in HIV patients with an extensive decline of CD4 cell count (< 100/microl). HIV patients who had received antimicrobial or H2-antagonizing drugs within 12 months prior to the study commencement also were found to have a remarkably decreased frequency of HP infections independently of their CD4 cell count. No association between HP infection prevalence and patients age, sex, risk group and the type of their antiretroviral treatment was found.We concluded from these results that the decreased HP infection prevalence in HIV patients may, apart from frequent antibiotic treatment, be correlated to the stage of HIV-mediated immune suppression.