Twelve biopsies of clinically normal oral mucosa taken from HIV seropositive patients have been investigated by means of light‐ and electron microscopy. Vascular abnormalities were found in all biopsies, regardless of the clinical stage of the HIV infection. In particular slit‐like vascular channels, sparseness of intercellular junctions and swollen, protruded endothelial cells with an increased quantity of Weibel‐Palade bodies were noticed. These findings were similar to those described in lesions of early stage Kaposi's sa