Hypophysectomized [male] rats, 24-90 days old, were treated with prolan, hypophyseal synergist, or a combination. Testes of those treated immediately after operation were maintained or caused to grow; all had spermatozoa. Repair of testicular tubular epithelium always took place after 40-day delay in treatment after operation. Hypophyseal synergist alone did not affect seminal vesicles or interstitial tissue. Prolan alone produced increase in Leydig tissue and repair in seminal vesicles. The combination caused still greater development of accessories.