Quercetin is one of the most ubiquitous flavonoids in foods of plant origin. Although quercetin is generally considered to provide protection against oxidative injury, recent studies have shown to be cytotoxic to many cell types. We intended here to determine whether quercetin protects against H2O2-induced toxicity and/or affects viability of rat mixed glial cells. The cells were obtained from 1-3 day olds rat brains and incubated in a humidified atmosphere of 5% CO2, at 37 degrees C in flasks. In the quercetin groups, different quercetin concentrations (1, 10, 50, 75 or 100 mu M) were applied alone for 24 h. For H2O2 cytotoxicity group, the glial cells were treated for 3 h with 100 mu M H2O2 which induced 75% cell death. In another group, the cells were treated with 100 mu M H2O2 plus respective quercetin concentrations simultaneously for 3 h, the medium was removed and refed for 24 h. MTT test was then applied and statistical significance was ascertained by one way analysis of variance, followed by Tukey's multiple comparison test. Quercetin starting from 50 mu M decreased the glia survival significantly. In H2O2 plus quercetin co-treated groups, both 75 and 100 mu M quercetin attenuated toxic effect of H2O2 by 15%. In conclusion, quercetin both partially protects H2O2-induced gliotoxicity and decreases rat glial cell viability in primary culture.