A necrotic torted testis left in the scrotum affects the contralateral testis, resulting in depressed fertility. It was suggested that testicular torsion provoked a systemic response of an immunologic nature. In order to prove this theory, 56 rats were operated. Ten had a sham operation, in 17 a testis was torted and excised after 24 h, and in 29 a testis was torted and excised after 24 h, and in 29 a testis was torted but left in situ till the sacrifice. Antisperm-antibodies were not found in any phase of the experiment in the sham group. Using indirect immunofluorescence, antisperm-antibodies were found in the sera of 8/17 rats of the orchiectomy group and in 24/29 of the detorted group. In the direct immunofluorescence study, all the antibodies were localized in the tail of the spermatozoid. The antisperm-antibodies disappeared after 3 to 6 months.