Either active or passive smoking has been reported as a risk factor for coronary heart disease. Several studies showed decreased plasma ascorbic acid (AA) in smokers. We examined plasma AA levels and its redox status (ratio of dehydroascorbate (DHA) to total AA) in smokers and nonsmokers regularly exposed to environmental cigarette smoke (passive smokers). The study population consisted of 55 healthy males (aged 43.7 ± 6.3 yr) comprising 25 active smokers (with consumption of ≥ 15 cigarettes / day for ≥5 yr), 15 passive smokers (with ≥ 30 h / wk environmental cigarette smoke exposure), 15 nonsmokers (with no evidence for cigarette smoke exposure). After 12 hours fast and abstinence from smoking, blood samples were obtained from the subjects. Plasma AA levels were measured by high-performance liquid chromatography. DHA levels were determined by subtracting the values of AA from that of total AA levels after addition of dithiothreitol as a reducing agent. Plasma AA levels were significantly lower in active smokers than overall nonsmokers (6.4 ± 2.7 vs 8.2 ± 2.9 μg/ml, p < 0.05, respectively). Although no differences in plasma DHA levels were found in three groups, DHA/total AA ratio (%DHA) was significantly higher in active and passive smokers than non-exposed nonsmokers (12.3, 10.4 vs 4.7%, p < 0.05, respectively). These results indicate that passive smoking, as well as direct inhalation of cigarette smoke, affects the redox status of plasma AA.