In vitro adherence of Streptococcus pneumoniae to buccal epithelial cells was assessed among smokers (51.9 +/- 20.8) and non-smokers (24.7 +/- 9.6) and found to be significantly higher (P less than 0.001) in smokers. The higher incidence of respiratory tract infection in smokers may be related to the enhanced adherence and better colonization of this bacterium in the throat.