The elimination of caffeine from saliva was compared in groups of healthy smokers (n = 13) and nonsmokers (n = 13). Mean caffeine t1/2 in smokers (3.5 hr) was shorter than that in the nonsmokers (6.0 hr). The body clearance of caffeine in the smokers (155 +/- 16 ml . kg-1 . hr-1) was greater than that in the nonsmokers (94 +/- 18 ml . kg-1 . hr-1) (p less than 0.05). No significant difference was noted in the apparent volume of distribution in smokers (720 +/- 67 ml . kg-1) and nonsmokers (610 +/- 80 ml . kg-1). These differences probably reflect the induction of hepatic aryl hydrocarbon hydroxylase (AHH) activity in smokers. The increased clearance of caffeine by smokers may contribute to the higher consumption of coffee reported to occur in this group.