Transplantation into man of whole, or parts of, testicles as a therapeutic measure has been practiced to some extent by surgeons and urologists in both this and foreign countries. The premises for such procedures have been the loss of both testicles through injury or removal, or, more often, an assumed hypogonadism in a patient whose own organs were diagnosed as below normal function in the production of their internal secretions. The latter diagnosis is of particular interest because of the fact that up to the present time there have been no recognized means of detecting a low male hormone state in man; ephemeral indexes have been assumed to be indicative of this condition just as equally elusive and questionable psychic reactions have been assumed to indicate increases in hormone titer after certain manipulations. A review of the literature on testis transplantation into man during the last twenty years acquaints one