Cigarette smoke is known to generate free radicals by various mechanisms. In this study involving 30 non-smokers and 30 smokers, we show that urinary excretion of 5-(hydroxymethyl) uracil (HMUra) was not different in the two groups (6.54+/-2.07 vs. 6.70+/-1.68 nmol/mmol creatinine). In contrast, 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dGuo) excretion increased by 16% (1.16+/-0.35 vs. 1.35+/-0.50 nmol/mmol creatinine, p = 0.039). Results concerning 8-oxo-dGuo are in agreement with those of previous studies. We observed significant multiple correlations between HMUra and creatinine (r(p) = 0.44), BMI (r(p) = -0.27) and nicotine derivatives (r(p) = 0.26). Multiple correlation analysis showed relations between 8-oxo-dGuo on the one hand, and: creatinine (r(p) = 0.36), nicotine derivatives (r(p) = 0.29), BMI (r(p) = -0.24) on the other.