The effect of pituitary homografts on the accessory sex organs and hormonal levels were studied in Wistar mature male rats. Grafted rats were further divided into four experiments: rats were bled once daily via a jugular vein cannula for seven days to investigate when serum prolactin began to rise after transplantation. rats were decapitated on the seventh day after transplantation to test whether 7 days were long enough to show the effect of pituitary grafts on the weight of prostate and seminal vesicles. rats were orchiectomized or orchiectomized and adrenalectomized on the seventh day after transplantation and then decapitated 4 weeks later to test a long term action of pituitary grafts and hormonal levels on the accessory sex organs without androgen. Rats grafted with several pieces of muscle were used as controls in each experiment. The initial rise in serum prolactin level was observed on the fourth day after pituitary transplantation, and then a higher serum prolactin level was maintained thereafter. Despite the higher prolactin level in the pituitary-grafted rat than in the control, no significant differences from the control in the weight of prostates and seminal vesicles and adrenal gland and the concentrations of serum luteinizing hormone (LH) and follicular stimulating hormone (FSH) were measured. This result showed that the weight of accessory sex organs was not affected by a higher serum prolactin within seven days.(ABSTRACT TRUNCATED AT 250 WORDS)