Often degenerative changes in the testicular tissue of men may be caused by a specific inflammatory process. This can be mumps orchitis following parotitis epidemical. Thirty-four patients with mumps orchitis and azoospermia were investigated. We have found through histological research of the rest patients a different degree of decreased spermatogenesis or a total lack of germinal cells in the tubules of the testis, maturation arrest of germ cells or Sertoli only syndrome. The intensity of the histochemical reaction of NADH-TR and LDH-activity showed strong expression in the basal compartment of the seminiferous tubules and in the Leydig cells. The strongest reaction was observed in the Sertoli cells. In the sections of patients with total spermatogenesis no difference was observed regarding NADH-diaphoreses and LDH-enzyme activity, whereas in cases with maturation arrest at primary spermatocyte and spermatid stage of spermatogenesis enzymehistochemical activity was localized in Sertoli cells of seminiferous tubules.