To study the spermatogenic potential of postpubertal undescended testis, the 3H-thymidine and 14C-uridine incorporations into normally descended and inguinal undescended testes were examined. The results suggest that DNA synthesis by the inguinal undescended testis is remarkably inhibited but, on the contrary, RNA synthesis is not. The cell-proliferative ability of postpubertal undescended testis may be impaired in spite of the retention of cell viability in the testis.