Plasma prolactin was measured in fourteen fertile women during a control cycle and during treatment with two different types of contraception. Ten of the women received a low dose combination type oral contraceptive, while the other four had a d-norgestrel-releasing intrauterine device (d-Ng-IUD) insereted. Plasma samples were corrected in the follicular and luteal phases during the control cycle and the treatment cycles in the d-Ng-IUD-group. In the oral contraceptive group, the samples were collected before treatment, three weeks, and again three months after the beginning of treatment. The results in the different grolups and the different phases of the cycles were compared, but no significant differences were found.