Four metrics were used to assess exposure to environmental tobacco smoke (ETS) for a probability sample (n = 152) of elementary school-age children in two economically disadvantaged neighborhoods: a) caregiver responses to a baseline questionnaire (BQ) about smoking status and behavior; b) 48-hr time-activity (T-A) data on location and time spent by children in the presence of tobacco smoke; c) total urinary cotinine as a marker for nicotine uptake; and d) urinary NNAL [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol] + NNAL-Gluc [4-(methylnitrosamino)-1- (3-pyridyl)-1-(O-beta-D-glucopyranuronosyl)butane] as a marker for uptake of the tobacco-specific lung carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Consistent differences in ETS exposure by ethnicity and race were observed. Although data were insufficient to determine differences for NNAL + NNAL-Gluc, BQ responses, T-A data, and cotinine levels all indicated that average ETS exposure was highest for African-American children, moderately high for those designated "other" (white, Southeast Asian, Native American), moderately low for Hispanic children, and lowest for Somali immigrant children. For example, in February 2000, mean cotinine levels were 14.1 ng/mL for African Americans, 12.2 ng/mL for other, 4.8 ng/mL for Hispanics, and 4.4 ng/mL for Somalis. The BQ and T-A data together were reasonably good predictors of total cotinine levels (adjusted r2 = 0.69), and based on limited data, measured total cotinine values were a relatively good predictor of NNAL + NNAL-Gluc (adjusted r2 = 0.73). The results suggest that when children are exposed to ETS primarily in their homes, questionnaires and T-A logs might be effective screening tools for identifying those likely to experience higher uptake of nicotine.