BACKGROUND Nevirapine (NVP) is a non-nucleoside reverse transcriptase inhibitor used in the treatment of HIV infections and has been reported to be toxic to the male reproductive system. This study was designed to evaluate the ameliorative effects of kolaviron (KV), a biflavonoid from Garcinia kola, on NVP-induced testicular toxicity. METHODS The adult male Wistar rats were given two and four times therapeutic doses of NVP (NVP-2T and NVP-4T; 18 and 36 mg/kg NVP) alone or in combination with KV (200 mg/kg). NVP was given daily, whereas KV was administered five times in a week by oral gavage. RESULTS Treatment with NVP did not alter the body weight gain and relative weight of testis of the rats. NVP-4T significantly (p<0.05) decreased the sperm motility, protein content, and live-dead ratio and also increased the percentage sperm abnormalities of the rats. Although NVP-4T significantly increased sperm abnormalities, it has no effect on epididymal sperm count. Also, NVP-4T caused a significant (p<0.05) elevation of serum aminotransferases and γ-glutamyl transferase activities. In addition, NVP-4T significantly (p<0.05) decreased the levels of testicular superoxide dismutase, catalase, glutathione S-transferase, and glutathione with marked elevation of malondialdehyde (index of lipid peroxidation) in the rats. In contrast, NVP-2T did not produce an adverse effect on the biochemical indices studied in testes and sperm of rats. Supplementation with KV significantly ameliorated the biochemical changes caused by NVP-4T. CONCLUSIONS Taken together, KV reversed the adverse effects of NVP-4T on testicular antioxidant enzymes and markers of oxidative stress in the rats.