Objective: To evaluate the immunologic etiology in unilateral testicular torsion, an experimental study in rats was carried out. Materials and Methods: 75 adult Wistar rats included in the study program were divided into six different groups according to a torsion-detorsion procedure. Torsion degree was kept constant for all animals (720 degrees). Anti-rat immunoglobulin G (IgG) antibodies against spermatozoa antigens were identified in contralateral testicular tissue after 1 month following detorsion and/or orchiectomy of the twisted testicle. Results: We revealed antibody formation in animals subjected to unilateral torsion for 12 and 24 h, which then followed by detorsion of the testicle, IgG was identified especially on basal membrane of the tubules. Conclusions: As the controversy on the exact mechanism of testicular dam age in unilateral torsion still continues, our findings showed that a possible immunological etiology may play an important role in this respect. Copyright (C) 1999 S. Karger AG, Basel.