BACKGROUND The reversibility of reproductive toxicity induced by the Nigerian Bonny light crude oil (BLCO) was investigated in rats. METHODS Adult male Wistar rats were orally treated with BLCO at 0, 50, 100 and 200mg kg(-1) for 21 days. One-half of the rats were sacrificed on day 22 while the remaining one-half stayed additional 21 days without treatment. RESULTS While sperm quality was compromised in dose-dependent manner, testis histopathology was only evident at 200 mg kg(-1) after 21 days. BLCO significantly decreased activities of superoxide dismutase, catalase and glucose-6-phosphate dehydrogenase but markedly elevated gamma glutamyltransferase and glutathione S-transferase activities as well as malondialdehyde, hydrogen peroxide and glutathione levels in both testes and sperm. Most of the above-mentioned parameters were consistent in animals from withdrawal experiment. CONCLUSIONS Taken together, BLCO exposure impaired fertility via increased oxidative stress and was not reversible upon withdrawal of treatment within the time course of investigation in male rats. BLCO exposure poses a risk for impaired fertility and its contribution to infertility in the Nigerian male population may not be excluded.