To investigate the influence of acute normovolemic hemodilution (ANH) on endocrine parameters in orthopedic surgery patients, 20 patients scheduled for total prosthetic replacement of the hip under epidural anesthesia with bupivacaine 0.5% were randomly allocated to the following groups: ANH group, (about 7.5 ml/kg body weight within 30 min) during substitution with 6% HES 200/0.5; Control group (without hemodilution). During a period before the onset of anesthesia and on the 1st day after the operation, MAP, HR, plasma concentrations of adrenaline and noradrenaline (by HPLC/ECD), and of ADH, ACTH and cortisol (by RIA) were determined at 8 points, as were glucose, lactate and free glycerol. Biometric data were comparable between the groups. MAP was significantly higher in the ANH group, and the intraoperative decrease was less pronounced. Adrenaline, ACTH, and cortisol revealed no specific influence of ANH and remained within the normal range in both groups. Noradrenaline was above the normal range in both groups and increased slightly (about 20%) during ANH. ADH was significantly higher in the control group. No specific influence of ANH was found with respect to glucose, lactate and free glycerol. In conclusion, ANH had no negative effects on the endocrine stress response during orthopedic surgery under epidural anesthesia. Sympatho-adrenergic reactions were only moderate and tolerable, even for patients with compensated cardiovascular disorders. Slight increases in endocrine parameters in the perioperative period documented adequate stress protection with epidural anesthesia.