Changes in serum hormone concentrations induced by surgical trauma were studied by determination of cortisol, dehydroepiandrosterone (DHA), dehydroepiandrosterone sulphate (DHAS), estrone (E1) and prolactin in 25 postmenopausal women. Blood samples were collected before, during and after mastectomy (14 women) and cholecystectomy (11 women). A slight peroperative increase in DHA preceded a marked postoperative decrease whereas no significant changes were seen concerning DHAS. The posttraumatic increase in cortisol values was delayed in relation to that of DHA, reaching its maximum on the first postoperative day. There was a pronounced postoperative increase in estrone which was only slightly (r = 0.3) correlated to the concomitant changes in the serum levels of DHA and cortisol indicating that other factors than increased availability of precursor steroids might influence this change. Prolactin levels showed an about fourfold peroperative increase and were normalized on the first day after surgery. No significant differences in preoperative values were seen between the groups although generally more pronounced and retarded changes were seen after cholecystectomy than after mastectomy.