Levels of vitamin C, ceruloplasmin, transferrin and albumin in serum, and glutathione in red blood cells were investigated in 40 patients with asthma to determine whether their antioxidant status was different from healthy subjects. Serum vitamin C and albumin levels were lower in the patient group (36.91+/-12.50 microM and 46.2+/-3.0 g/L, respectively) than in 43 healthy volunteers (53.38+/-13.06 microM and 48.8+/-2.1 g/L, P<0.001 and P<0.05, respectively). However, erythrocyte glutathione and serum ceruloplasmin levels were higher in the patient group (0.59+/-0.11 mol/mol hemoglobin and 442+/-73 micromol/L, respectively) than in controls (0.49+/-0.09 mol/mol hemoglobin and 308+/-47 micromol/L, P<0.001 and P<0.001, respectively). No difference was observed in transferrin levels between the groups. The results suggest that reactive oxygen species may be a contributing factor in patients with asthma, causing changes in serum vitamin C, ceruloplasmin and erythrocyte glutathione levels.