Pituitary glands grafted under the kidney capsule provide a continuous supply of prolactin due to the absence of hypothalamic inhibitory factor. Increase in the level of prolactin in the rat may affect availability of hormone for reproductive function. Single pituitaries were transplanted under the kidney capsule of male rats. After six weeks of the transplant, the recipient rats were sacrificed and trophic activity of testosterone and intratesticular functions were assessed. The weights of ventral prostate and seminal vesicles, full and empty, showed significant increase from the control value. The activity of beta-glucuronidase in kidney, an androgen inducible enzyme, also increased in comparison with the control value. Incorporation of 32P in the nucleic acid fraction showed an increase. The increased rate of testosterone production and an alteration in spermatogenesis was associated with increased activity of acid phosphatase and decreased activity of beta-glucuronidase. The active mediation of lysosomal enzyme in testicular function as altered by prolactin was indicated.