Background: Recent years' usage of thinner by the young generation as a drug constitutes a serious problem in the society. Due to common usage in the industrial sector, most people are affected from the manufacturing process to the consuming phase. Aim: Because of these reasons, this project has been preferred to research the effects of thinner on oxidant and antioxidant status. Methods: Totally 46 rats were included in the study. Thirty six rats were separated into six groups with 10 rats in a control group. The first group inhaled thinner for 2 weeks, and the other groups were exposed to thinner for 4, 6, 8, 10 and 12 weeks for 1 h twice a day. On the mentioned duration, rats were autopsied. Lung tissues malondialdehyde (NIDA), glutathione (GSH) levels and superoxide dismutase (SOD) activities were determined to designate the oxidant-antioxidant balance. Results: We observed an increase in MDA values both in the acute and the subacute periods. In the chronic period by the consuming of lipid peroxidation products, MDA values decreased and as the oxidative stress continued MDA values again increased. We observed that especially GSH values that has antioxidant feature, decreased until 6 weeks in order to compensate lipid peroxidation products. In the consuming period of lipid peroxidation, the values became fixed and later, these values again increased. There was no relationship between the changing values of MDA and SOD. Conclusions: Thinner is an agent that causes oxidative stress and inhalation of high doses of thinner causes harm to the respiratory system. As there are few reports in the literature on long-term effects of thinner inhalation, more studies might be necessary. (C) 2004 Elsevier B.V. All rights reserved.