160 oral swabs of 149 HIV-infected patients and 168 swabs of 166 controls were cultured to detect a possible colonization of the oral cavity with yeasts and Enterobacteriaceae. In 5.0% of the HIV-infected patients and in 4.8% of the controls different species of Enterobacteriaceae were found. Yeasts were always associated with Enterobacteriaceae in the group of HIV-infected patients. Clinically, different oral lesions were seen in the study group. A correlation between the nature of these lesions and the presence of Enterobacteriaceae could not be found. A possible pathogenic role of the Enterobacteriaceae associated with these oral lesions is yet uncertain and remains to be established by further studies.