The anti-testicular action of PMHI was investigated in a wild rodent, the bandicoot rat. Bandicoots were given a single subcutaneous injection of this compound at a dose of 150 mg/kg and were killed 2, 10, or 30 days later. PMHI induced marked and rapid testicular regression with complete arrest of spermatogenesis by day 10 such that the seminiferous tubules contained only a ring of Sertoli cells with few spermatogonia. This was also reflected by a severe depletion of the number of sperm in the cauda epididymis. However, by day 30 after PMHI injection, testicular histology indicated restoration of spermatogenesis in parallel with the time schedule of germ cell development. The results indicate that PHMI produces a reversible anti-spermatogenic effect in the bandicoot rat which appears to be time dependent.