Ninety female Balb/c mice were used. The animals were allocated to evenly six groups. While the first group was maintained as control. Groups 3, 4, 5, and 6 were administered 750 ppm, 1500 ppm, 3000 ppm, and 6000 ppm of N-acetylcysteine, respectively, for a period of 15 days. After day 15. Groups 2-6 were administered sodium fluoride, containing 100 ppm fluoride in drinking water, for another 15 days. Plasma malondialdehyde (MDA) levels and erythrocyte superoksid dismutase (SOD) and catalase (CAT) activities were determined at the beginning of the trial and on days 15 and 30. According to the data obtained in the present study, N-acetylcysteine, when administered at the indicated doses, did not produce a significant alteration in any of the three parameters investigated. On the other hand, while the plasma MDA level was determined to have increased significantly, erythrocyte SOD and CAT activities were ascertained to have decreased significantly in the group, which was administered sodium fluoride alone on day 30. In the groups, which were administered N-acetylcysteine prior to sodium fluoride, however, it was observed that, after sodium fluoride administration, plasma MDA levels and erythrocyte SOD and CAT activities drew closer to the values of the control group. (C) 2010 Elsevier Ltd. All rights reserved.