BACKGROUND: Nondaily smoking has increased among current U.S. smokers in the past decade and is practiced by a significant percentage of smokers. Although research in nondaily smoking has grown, little is known about levels of exposure to tobacco toxicants among nondaily smokers and their variation across ethnic groups.

METHODS: We examined urinary levels of cotinine and a tobacco-specific nitrosamine (NNAL) in community participants. Associations between the biomarker data and smoking characteristics were evaluated using Spearman's correlation analysis.

RESULTS: Participants were 28 Blacks, 4 Latinos, and 25 Whites who smoked at least 1 cigarette on 4-24 days in the past 30 days. Participants averaged 3.3 (SD = 2.1) cigarettes per day (cpd) on days smoked, smoked an average of 13.0 (SD = 5.4) days in the past month, and smoked nondaily for 10.5 (SD = 10.5) years. Median levels of creatinine-normalized cotinine and NNAL were 490.9ng/mg and 140.7 pg/mg, respectively. NNAL and cotinine were highly correlated, r = .84; NNAL and cotinine were modestly correlated with cpd, r = .39 and r = .34 (all p values

CONCLUSIONS: Our findings demonstrate that nondaily smokers are, on average, exposed to significant levels of nicotine and carcinogenic nitrosamines, with exposures of 40%-50% of those seen in daily smokers. This level of exposure suggests a significant health risk. Nicotine and carcinogen exposure is most closely related to number of cigarettes smoked per day but not to number of days per month of smoking.