Inflammatory reactions to microbial infections may cause male infertility. The mechanisms of inhibition of spermatogenesis can be studied in vitro using rat Sertoli cells. Bacterial lipopolysaccharides (LPS) induce acute inflammations. So LPS treated Sertoli cells can be used to test for new therapeutic compounds. The present study aimed to investigate the protective efficacy of dl-alpha-lipoic acid (LA) on lipopolysaccharide (LPS)-induced oxidative stress in adult rat Sertoli cells. Sertoli cells were divided into 4 groups. Group I served as a control incubated with water (vehicle). Groups II and IV were incubated with 100 microM LA for 24h before incubating Groups III and IV with 50 microg/ml lipopolysaccharide (LPS) for 12h. In Group III cells (LPS-treated, no LA) the lactate concentration was decreased whereas hydrogen peroxide production and lipid peroxidation were significantly increased. Moreover, the activities of antioxidant enzymes such as superoxide dismutase, glutathione peroxidase, catalase, glutathione-S-transferase, glutathione reductase were reduced. The concentrations of antioxidant molecules such as reduced glutathione and vitamin C were significantly decreased. The activities of enzymes normally elevated in Sertoli cells, gamma-glutamyl transpeptidase and beta-glucuronidase, were significantly decreased. Treatment with LA (100 microM) for 24h before LPS-treatment (Group IV), prevented these changes in enzyme activities and metabolite concentrations. Therefore, LA may have a cyto-protective role during LPS-induced inflammation in adult rat Sertoli cells.