Polycyclic aromatic hydrocarbons (PAHs) are mutagenic in somatic cells, while it remains unclear whether PAHs induce mutations in male germ cells, subsequently increasing health risks in offspring. Although results from the classical specific locus test are negative or inconclusive, recent studies with environmentally exposed animals suggest that PAHs are mutagenic in sperm cells. Therefore, we studied whether benzo(a)pyrene was able to induce gene mutations in testis and sperm cells of wild type (Wt) and Xpc(-/-) mice containing the pUR288 lacZ reporter gene. Mice were exposed to benzo(a)pyrene (13 mg/kg bw, 3 times per week) during 1, 4 or 6 weeks and sacrificed 6 weeks after the final exposure to obtain mutations in sperm derived from benzo(a)pyrene-exposed spermatogonial stem cells. The lacZ gene mutation assay was used to assess mutant frequencies in spleen, testis and mature sperm, and (32)P-postlabeling was used for the detection of DNA adducts in testis. Successful exposure was confirmed by a dose-related higher mutant frequency in spleen of Xpc(-/-) mice as compared to Wt mice. Mutant frequencies were also increased in all ethyl nitrosourea (ENU) exposed samples, which were used as positive control. Although benzo(a)pyrene-related DNA adducts were detected in testis, mutant frequencies were not increased . On the other hand, benzo(a)pyrene increased mutant frequencies in sperm of Wt mice, but not in Xpc(-/-) mice, after 6 weeks exposure. Therefore, we conclude that benzo(a)pyrene can induce gene mutations in spermatogonial cells of mice, but it remains to be elucidated whether these mutations can be transmitted to offspring.