Day/night profiles of serum GH, PRL, IGF-I, LH, FSH, testosterone (TT and FT), estradiol (E2) and SHBG were estimated in 12 acromegalic women with GH- and PRL-producing pituitary adenomas and 13 patients with GH-secreting pituitary tumors before and 3 months after transsphenoidal adenectomy. All the subjects studied have had irregular menstrual cycles. Blood for profile determinations was drawn from a peripheral vein at 3 h intervals for three 24 h periods (starting at 08.00). Before surgery all acromegalic women had high mean 24 h GH and IGF-I levels (with irregular peaks) even in the absence of hyperprolactinemia. Postoperative mean 24 h GH level was still high only in 5 out of 25 women studied, and that of IGF-I in 10 of these patients. In 12 acromegalic women with preoperative hyperprolactinemia and disturbed 24 h fluctuations postoperative 24 h mean level of PRL and its circadian rhythm were normal. Before surgery, the circadian variations of pituitary-sex hormone levels and SHBG capacity in serum were not impaired. However, mean 24 h levels of LH, FSH, TT, FT E2 and SHBG were altered mainly in patients with mixed type of GH and PRL producing adenomas. This may be related to the increased activity of GH/IGF-I axis on the one hand and to the excess of PRL on the other. The postoperative normalization of pituitary-sex hormone levels and SHBG capacity in serum was noted only in women with normal 24 h circadian variations of IGF-I levels.