Large segments of populations, including children, are exposed to environmental tobacco smoke (ETS), a risk factor for lung cancer and heart, circulatory and respiratory diseases. Recently, ETS was classified as a class A carcinogen by USEPA, as carcinogenic to humans by IARC (group 1) and by the National Toxicology Program of the US National Institutes of Health. Cotinine, a product of the metabolism of nicotine, is measurable in urine and, correlates strictly and directly to ETS exposure, therefore representing a well-known internal dose marker. Another marker of active tobacco smoking is the N-(2-hydroxyethyl) valine (HOEtVal) which results from the reaction between ethylene oxide (EtO) and the N-terminal valine of hemoglobin. The aim of this study was the evaluations of ETS markers, namely urinary cotinine and HOEtVal measured in blood in 100 children with ages ranging between 3 and 13 years. Experimental findings show that cotinine, as a specific internal dose marker, and HOEtVal, as a nonspecific biological effective dose marker, both depend on the passive exposure to ETS as well as on the active habit of smoking.