both active and passive smoking are regarded as risk factors for various diseases . to clarify the effects of active and passive smoking on plasma vitamin c levels and lipid peroxidation status 
 , we examined the plasma levels of ascorbic acid ( aa ) , its redox status [ ratio of dehydroascorbate ( dhaa ) to total aa ] , the levels of thiobarbiturate reactive substance ( tbars ) , and the levels of lipid peroxides ( lpo ) in smokers , nonsmokers , and nonsmokers regularly exposed to environmental cigarette smoke ( passive smokers ) . 
 the study population consisted of 149 healthy males : 75 active smokers ( consumption of > 15 cigarettes / day for more than 5 years ) , 36 passive smokers ( more than 10 hr / week exposure to environmental cigarette smoke ) , and 38 nonsmokers ( no cigarette smoke exposure ) . 
 there were no significant differences in plasma tbars and lpo levels among the three groups . 
 plasma levels of aa , the reduced form of vitamin c , were significantly lower in active smokers than in the combined nonsmoking groups ( 7.2 + /- 
 3.5 and 8.4 + /- 
 3.4 microg / ml , respectively ; p < 0.05 ) . 
 although no significant differences were found in plasma dhaa levels among the three groups , the ratios of dhaa to total aa were significantly higher in active and passive smokers than nonexposed nonsmokers ( 11.2 , 10.3 , and 7.1% , respectively ; p < 0.05 ) . 
 these results indicate that passive smoking , as well as direct inhalation of cigarette smoke , affects the redox status of plasma aa . in passive smokers , 
 the altered redox status of plasma aa suggests an oxidative stress.imagesfigure 1