The effects of apple consumption on plasma and erythrocyte antioxidant parameters of elderly subjects were investigated in this study. Fifteen elderly subjects (mean age 71.86 +/- 4.17) participated in the study. They consumed an apple a day for 1 month. Before and after this period, fasting blood samples were obtained, and oxidant (malondialdehyde [MDA]) and antioxidant (superoxide dismutase [SOD], glutathione peroxidase [GSH-Px], catalase [CAT], and antioxidant potential [AOP]) parameters were studied. MDA and AOP levels were studied in plasma, and SOD, GSH-Px, and CAT activities and MDA levels were measured in the erythrocytes. In the erythrocytes, GSH-Px and SOD activities were found to be higher (p < .001 and p < .01), but MDA levels were lower in the second samples relative to the first ones. In the plasma, AOP value was found to be higher in the second samples relative to first ones (p < .001). No differences were found, however, between the routine blood parameters such as total cholesterol, low-density lipoprotein cholesterol, very-low-density lipoprotein cholesterol, high-density-lipoprotein cholesterol, and triglyceride levels. The results show that consumption of apple leads to significant increases in the activities of some antioxidant enzymes and in the antioxidant potential values of the blood, and that decreases oxidation reactions in the body in significant amount. It is quite possible that reduced peroxidation processes owing to consumption of this fruit may play a part in some of their beneficial effects in the elderly subjects.