ABSTRACT: In an experimentally established model of torsion of the testis, morphological and immunological observations were evaluated on 180 Wistar rats. Torsion of the testis was carried out to observe in animals the biological phenomenon that naturally occurs in man. The effect of the twisted testis on the contralateral testis was carefully checked. The morphological observations revealed serious damage to the seminiferous tubules in the contralateral testis. In four rats, persistent infertility was observed as an effect of torsion. The infertility was confirmed by total atrophy of seminiferous epithelium in testis section. The cell-binding abilities of sera obtained from rats at different times after torsion were studied by cell-binding radioimmunoassay with different types of germinal cells. The presence of autoantibodies to epididymal spermatozoa was revealed in most cases, being a secondary effect of the thus-far unknown, nonspecific factors responsible for damage of the contralateral testis.