Increased levels of PROLACTIN in the BLOOD, which may be associated with AMENORRHEA and GALACTORRHEA. Relatively common etiologies include PROLACTINOMA, medication effect, KIDNEY FAILURE, granulomatous diseases of the PITUITARY GLAND, and disorders which interfere with the hypothalamic inhibition of prolactin release. Ectopic (non-pituitary) production of prolactin may also occur. (From Joynt, Clinical Neurology, 1992, Ch36, pp77-8).