Studies indicate that leptin is involved in not only energy expenditure and food intake, but also in protection against apoptosis, in inflammation and in stimulation of proliferation in many cell types. However, leptin treatment increases the oxidative stress in many cell culture studies. This contradiction evoked a question of whether leptin acts as an oxidant or antioxidant on glial cells. We investigated the effect of leptin on glial cell survival and hydrogen peroxide (H2O2)-induced toxicity in vitro. The survival rate of the cells was determined by using 3-(4,5-D-methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, thyazolyl blue (MTT) method. The cells obtained from the whole brain of 1 -3 day-old rat were treated with 1, 10, 100 and 1000 ng/ mL leptin for 24 or 72 h. Either the pretreatment of leptin alone for 5 h or leptin combined simultaneously with H2O2 or well known antioxidant glutathione (GSH) were applied to the cells. Malondialdehyde (MDA) levels were measured in cell lysates to which leptin was added for 24 h. The 100 and 1000 ng/ mL leptin treatment for 72 h increased the glial viability by 19% and 36%, respectively. The dose of H2O2 that killed 75% of the cells was determined as 100 mu M. GSH at different doses was applied as a positive control to the cells and the dose of 500 mu M completely eliminated toxic effect of 100 mu M H2O2. Either the pretreatment of leptin alone for 5 h or leptin combined simultaneously with H2O2 could not eliminate H2O2-caused toxicity. Furthermore, respective leptin doses did not change the glia MDA level. We suggest that leptin can increase glia survival dose dependently, but can not eliminate H2O2-induced oxidation in primary mixed glial cell culture.