An attempt was made to determine whether sulfur dioxide (SO2) inhalation at 10 ppm, 1 hr daily, for 30 days induces oxidant stress and whether vitamin E (40 mg/kg) together with vitamin C (200 mg/kg), administered intraperitoneally once in every 3 days, can reduce the damage in red blood cell membranes of guinea pigs. Malonyldialdehyde (MDA) levels, osmotic fragility ratios, and methemoglobin and sulfhemoglobin values were significantly higher in the SO2-treated group compared with the control group (P < 0.05), and marked decreases in MDA levels and osmotic fragility ratios were determined in the group treated with SO2 + antioxidant vitamins (P < 0.05). (C) 1995 Academic Press, Inc.