Nineteen young adult male smokers were compared to 19 adult male nonsmokers to determine if cigarette smoking resulted in any changes to anaerobic bacteria in dental plaque, to intraoral oxidation-reduction potential (Eh) levels, or to intraoral pH. There was no statistical difference between smokers and nonsmokers in the proportion of anaerobic bacteria found in dental plaque. There were no significant differences between smokers and nonsmokers with respect to the resting Eh in the floor of the mouth nor in the Eh in the region of buccal surface of the upper molars. The smoking of one cigarette resulted in a dramatic fall in Eh in both intraoral regions and this occurred in all subjects, both smokers and nonsmokers. The magnitude of this fall in Eh was similar in both groups. There were also uniform increases in pH, but these pH changes were much smaller in magnitude.