This prospective study investigated whether oral candidal carriage in HIV-infected patients was altered by pentamidine therapy. Repeated oral rinses were taken from 56 HIV-positive patients over a 2-year period. Oral candidal carriage was investigated in two groups of patients, one receiving prophylactic pentamidine therapy and the other not receiving regular prophylaxis. Patients receiving pentamidine had lower concentrations of Candida albicans intra-orally than patients who did not receive it. Furthermore, patients who received pentamidine at one stage of the study, but not another, also had lower concentrations of C. albicans intra-orally when receiving pentamidine. These findings indicate that pentamidine is useful as a local agent for prophylaxis against intra-oral candidosis in HIV-infected patients.