<prompt> Most of the testosterone secreted by the testes exists in the plasma in the form of ?Dihydrotestosterone bound to gonadal steroid-binding hormoneFree dihydrotestosteroneFree testosteroneTestosterone bound to sex-steroid-binding globulin  <response>: The majority of circulating testosterone is bound to plasma protein around 98, rather than existing in free form . Of this, a majority is bound to a specific sex or gonadal steroid-binding protein , and a minority is bound to albumin. Dihydrotestosterone is produced from testosterone in the tissues by a specific enzyme, 5-alpha-reductase, rather than circulating in bound or free form. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. 2012. Chapter 23. Function of the Male Reproductive System. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks Eds, Ganongs Review of Medical Physiology, 24e. 