The relationships between the serum levels of estradiol, progesterone and prolactin have been analysed in normal women in relation to age, to menstrual cycle, and in oral contraceptives users. We have been able to detect significant differences between the prolactinemia values during the cycle in different age groups as well as following oral contraceptives. A word of caution is presented for the evaluation of the prolactin blood level which should always be related to the physiological phase of the cycle and to the age of the subjects.