IN A STUDY on the effect of male sex hormones on benign prostatic hypertrophy in man, I also reported in 1939 the effect of this hormone on the human testis.1 These observations showed that a man would become temporarily azoospermic or sterile after the administration of this hormone. It was also noted in one man who was followed for a period of time after he became azoospermic that the number of spermatozoa far exceeded pretreatment numbers. This phenomena created a great deal of interest and curiosity, and as a result further observations have been made. Recently Heller and others2 reported the result of their testicular biopsy studies from androgenically normal men who were given testosterone propionate. In their studies they obtained testicular biopsies before the administration of this hormone, at the end of treatment and six to 17 months after treatment. They discovered that after the administration of