To evaluate the relationship between self-reported exposure to environmental tobacco smoke and saliva cotinine concentrations, we studied 186 nonsmokers. Each participant completed an exposure questionnaire, kept a daily exposure diary for 7 days, and provided a saliva sample for cotinine analysis. Salivary cotinine concentrations were measured using gas chromatography/mass spectrometry. Of the volunteers, 30% lived with one or more smokers, and 84% were regularly exposed to smokers at work. Eighty-three percent of the volunteers had detectable saliva cotinine concentrations (> or = 0.5 ng/ml) (median = 1.1; range = 0.5-7.4 ng/ml). Cotinine concentrations were related to exposure in the household and at the workplace. Volunteers who lived with smokers had significantly higher cotinine levels (median = 1.0; range = < 0.5-7.4 ng/ml) than those who did not (median = < 0.5; range = < 0.5-4.7 ng/ml). Volunteers who reported regular exposure at work had higher cotinine levels (median = 0.8; range = < 0.5-7.4 ng/ml) than those who did not (median = < 0.5; range = < 0.5-3.0 ng/ml). Cotinine concentrations were predicted by a regression equation that included the number of smokers at home and work and the number of minutes of exposure recorded in the daily diary (r2 = 0.29).