The composition of the bacterial flora in the upper respiratory tract is closely correlated with the type of pathogens recovered from the respiratory tract in patients. In intensive care patients, colonization of the oral cavity with Gram-negative organisms increases the risk of Gram-negative respiratory tract infection; the ability of bacterial cells to attach to buccal cells seems to play a central role in this correlation. Similar findings have been reported in chronic respiratory tract infections, including bronchiectasis and cystic fibrosis, with Pseudomonas aeruginosa colonization. This study was undertaken to determine the conditions best suited to in vitro detection of adhesion of P. aeruginosa to buccal cells. Use of brain-heart-infusion medium, incubation at 35 degrees C for 2 hours, and a bacterial concentration of 2 x 10(9) cells/ml were the factors correlated with improved detection of adhesion to buccal cells. Furthermore, attachment of bacteria to buccal cells was not found to vary across donors or over time in a given donor. Adhesion was independent of cell viability.