To evaluate the responsiveness of spermatogenesis in the normal human testis to human menopausal gonadotropin (hMG) and human chorionic gonadotropin (hCG), the DNA synthesis of spermatogonia was investigated using 3H-thymidine uptake by cultured tissue fragments of human testis with or without treatment with hCG and/or hMG. Two groups treated with different concentrations of hCG showed no difference in 3H-thymidine incorporation into testicular tissue compared with untreated control. In two other groups treatment with combined hMG/hCG in different concentrations induced significant changes in 3H-thymidine incorporation compared with control (p less than 0.01, p less than 0.01). Combined hMG/hCG treatment was effective in inducing spermatogenesis by normal human testicular tissue.