DNA methylation catalyzed by DNA methyltransferases (DNMTs) and histone deacetylation catalyzed by histone deacetylases (HDACs) play an important role for the regulation of gene expression during carcinogenesis and spermatogenesis. We therefore studied the cell-specific expression of DNMT1 and HDAC1 for the first time in human testicular cancer and impaired human spermatogenesis. During normal spermatogenesis, DNMT1 and HDAC1 were colocalized in nuclei of spermatogonia. While HDAC1 was additionally present in nuclei of Sertoli cells, DNMT1 was restricted to germ cells exhibiting a different expression pattern of mRNA (in pachytene spermatocytes and round spermatids) and protein (in round spermatids). Interestingly, in infertile patients revealing round spermatid maturation arrest, round spermatids lack DNMT1 protein, while pachytene spermatocytes became immunopositive for DNMT1. In contrast, no changes in the expression pattern could be observed for HDAC1. This holds true also in testicular tumors, where HDAC1 has been demonstrated in embryonal carcinoma, seminoma and teratoma. Interestingly, DNMT1 was not expressed in seminoma, but upregulated in embryonal carcinoma.