There are no published studies examining the effects of N-acetylcysteine (NAC) administration on the non-enzymatic defence systems in humans exposed to lead. In view of this, it was decided to measure the levels of uric acid (UA), albumin, bilirubin and alpha-tocopherol before and after treatment with NAC. An estimation was also made of the degree of oxidative stress by measuring the ferric reducing ability of plasma (FRAP), the levels of conjugated dienes (CD) and lipid hydroperoxides (LHP). Male employees who worked with lead were randomized into two groups. The first group included workers who were not administered any drugs (n=49), while the second group (n=122) consisted of workers who were treated with NAC at three different doses (200 mg, 400 mg and 800 mg) for 12 weeks. The administration of NAC (400 mg, 800 mg) resulted in significant decreases in the LHP levels. Similarly, a strong tendency toward lower levels of CD was observed in the same groups. The UA levels were significantly lower only in the group receiving the 200 mg dose of NAC. However, the alpha-tocopherol levels were significantly elevated after treatment with NAC (400 mg, 800 mg). NAC administration did not significantly affect the levels of bilirubin and albumin, but a tendency toward higher values was observed for FRAP. NAC reduced the extent of lipid peroxidation in a dose-dependent manner. Elevated concentrations of alpha-tocopherol may have enhanced the beneficial effects of NAC. Treatment with NAC may contribute to the restoration of non-enzymatic antioxidant reserves when administered to lead-exposed workers.