Prolactin (PRL), growth hormone (GH), placental lactogen (PL), chorionic gonadotropin (CG), estradiol (OE), progesteron (P4) and sex hormone-binding globulin (SHBG) were measured in serum throughout gestation in 9 women with PRL-producing pituitary adenomas. They had been treated at least 1 year with the dopamine agonist bromocriptine before pregnancy occurred. All women bore healthy babies of normal birthweight. Their PRL levels did not show the successive increase seen in normal pregnancies; serum PRL was unphysiologically increased in all patients up to the 20th week of gestation, whereafter PRL levelled off and fell within the normal range. Serum PL levels were lower in the women with prolactinoma compared to healthy pregnant women, despite normal placental weight. The serum GH levels in the patients determined with an immunoassay based on a monoclonal antibody, were low or nondetectable, similar to healthy pregnant controls. In contrast, high molecular weight GH in serum as determined with a monoclonal antibody which also recognizes PL appeared to be increased in comparison with healthy pregnant women. The serum leels of CG, OE, P4 and SHBG were all within the normal range. These results show that the unphysiological secretion of PRL in pregnant women with PRL-producing pituitary adenomas is associated with decreased serum levels of PL.