In this thesis some effects of PRL on reproductive functions have been investigated PRL-secreting pituitary adenoma. animal model has been used: For in men with a comparison an In. rats hyperprolactinemia has been induced by sub-cutaneous inoculation of a PRL- and ACTH-secreting transplantable pituitary tumor.. The local effects of PRL on testicular functions have been studied by implantation of a pituitary in a testis. The symptoms of hyperprolactinemia in men with a pituitary adenoma are; as indicated ln many reports (Chapter l), mostly due to local effects of the tumor on para- and suprasellar tissues. Patients may present with headache, impaired vision, visual field defects, paresis of the eyemuscles and hypopituitarism. Loss of libido and potency, which symptoms may retrospectively be present for a long period, are considered by many authors to be typical feattures for male hyperprolactinemia. Gynecomastia and galactorrhea are uncormnon findings, respect to function of triuch of the research the hypothalamic-pituitary- testicular axis in hyperprolactinemic uen reported over the past few years is still controversial. The basal serum levels of LE and FSH may be normal or decreased and their response to LRH may be normal or blunted. Serum testosteron levels have been found subnormal, even in the presence of normal basal and LRH-stimulated LH and FSH levels. Furthermore serum testosterone levels may show a normal response to the administration of hCG. It is difficult to draw conclusions from the data present.ed in the various papers since most of the reported series comprised men with macroadenomas or men who had been treated before the time of presentation