Attachment of bacteria to tonsillar epithelium during acute tonsillitis. Epithelial cells were scraped from the tonsillar surfaces of 15 patients with current acute tonsillitis (AT) and of 15 individually matched healthy persons. The cellular mixture was stained with acridine orange and bacteria seen to be attached to the epithelial cells under the fluorescent microscope were calculated. Conventional bacterial culturing was also performed simultaneously. Significantly more bacteria were attached to epithelial cells from the AT group than from the controls (greater than 10 attached bacteria per cell p = 0.0103, greater than 50 attached bacteria per cell p = 0.0212). In vivo determination of bacteria attached to epithelial cells offers prospects of gaining a better understanding of the aetiopathogenesis of acute tonsillitis. 