 exposure to environmental tobacco smoke ( ets ) , which is largely composed of the sidestream cigarette smoke , has been implicated in increased incidence of cancer among nonsmokers . 
 the present study was conducted to compare the potential of mainstream and sidestream cigarette smoke to induce dna adducts in mice . 
 groups of female c57bl and dba mice were exposed twice daily for 65 - 70 weeks to mainstream or sidestream smoke from the university of kentucky reference cigarettes ( 2r1 ) in a nose - only exposure system . 
 animals received a total particulate matter dose of about 16 and 6 mg / kg body weight / exposure and exhibited blood carboxyhemoglobin levels of about 16 and 34% , for mainstream and sidestream smoke - exposed groups , respectively . 
 pulmonary aryl hydrocarbon hydroxylase ( ahh ) activity was induced by about 2- to 3-fold in both mainstream and sidestream groups of c57bl and in mainstream smoke - exposed group of dba mice , but not in sidestream smoke - exposed dba mice . 
 an analysis of total dna adduct levels by the 32p - postlabeling assay showed a significant ( 12- to 25-fold ) increase in the magnitude of preexisting lung dna adducts in both mainstream and sidestream smoke - exposed c57bl and dba mice . 
 smoke exposures did not affect the total preexisting dna adducts in liver of either strain . 
 it is concluded that both mainstream and sidestream smoke are capable of enhancing preexisting dna adducts in the lungs of chronically smoke - exposed mice.imagesfigure 3 . 
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