Forty-seven patients have been reviewed 2-10 years after torsion of the testicle. Thirty-six (77 per cent) were found to have abnormalities of exocrine or endocrine gonadal function. None showed evidence of testicular autoimmunization using standard assays of sperm agglutination and immobilization by serum or seminal plasma, and the serum mixed agglutination reaction (MAR) test. In addition, 11 cases of acute torsion were followed at intervals for 3-6 months after surgery, but no evidence was observed of the transient development of sperm antibodies. Our findings confirm poor gonadal function after torsion, but do not support the recent suggestion that it is caused by autoimmunization.