The testis, the epididymis and the prostate are immunologically suppressed organs in which allogeneic tissue grafts can survive for a long time. In the present study, morphological features of these three organs after systemic administration of immunopotentiators was investigated in mice to determine whether or not this treatment can affect their immunosuppressive circumstances. The animals were intravenously injected with adjuvants, Bordetella pertussigens, then killed 7-10 days later for histological examination. The results showed that the testicular interstitium was completely free from leukocyte infiltration but that the accessory glands (the prostate, the coagulating gland and the seminal vesicle), the vas deferens, the epididymis and the ductuli efferentes received extravasation of leukocytes into their interstitial tissues. This indicates that the testis is resistant to leukocyte infiltration compared with the epididymis and the prostate.