BACKGROUND We have previously demonstrated that quinine is a testicular toxicant in Sprague-Dawley rat. OBJECTIVE To describe the changes in the testicular levels of testosterone and lipid peroxidation secondary to quinine and ascorbic acid administration in rats. METHODS Twenty male Sprague-Dawley rats per group were assigned to one of three treatment groups: 0 mg quinine and 0 mg ascorbic acid/kg body weight (control); 10 mg quinine/ kg BW; and 10 mg quinine plus 0.1 mg ascorbic acid/kg BW. Rats were intramuscularly administered their respective doses of quinine five days in a week and ascorbic acid three days in a week for eight weeks. All the animals were sacrificed at the end by decapitation. Seminal analysis was performed on tubular fluid from caudal epididymides. Evaluations were made for testicular levels of testosterone and lipid peroxidation through malondialdehyde (MDA). Testicular specimens were also processed for histology under light microscopy. RESULTS Quinine significantly (p < 0.01) increased free radicals (from elevation of MDA) and decreased testosterone in the testis compared with those of the control group and those treated with a combination of quinine and ascorbic acid. The semen of rats treated with only quinine demonstrated a significantly (p < 0.001) lower sperm concentration and motility compared to the controls and those treated with quinine plus ascorbic acid. Microscopic examination of cross-sections of seminiferous tubules also showed that ascorbic acid partially protected against quinine -induced testicular effects. CONCLUSIONS Ascorbic acid has beneficial effect and protects against quinine-induced testicular reduction of testosterone.