The exocrine and endocrine functions of the testis were assessed in 67 patients a median of 4.0 years after unilateral torsion (range 3 months-12 years). Of 54 patients who underwent orchidopexy, some atrophy of the affected testis developed in 46; the degree of atrophy was significantly correlated with the duration of torsion (r = -0.56, p less than 0.001). The remaining 13 patients had undergone orchidectomy after a mean duration of torsion of 71 h. Seminal analysis was abnormal in 44 of 51 patients tested (86%), and the low total motile sperm count correlated with the duration of torsion (r = -0.53, p less than 0.001). Sperm counts were much lower in men with torsion for longer than 8 h than those with a shorter period of torsion (median 7.2 X 10(6) v 83.5 X 10(6); p less than 0.00003). Serum levels of luteinising hormone, prolactin, testosterone, and follicle-stimulating hormone were generally within normal limits. An acute ischaemic episode affecting only one testis causes bilateral loss of exocrine function in most patients, while endocrine function is preserved.