The effect of clonidine (4.5 micrograms kg-1) on haemodynamics and hormonal stress responses was evaluated in 21 female patients undergoing breast surgery. The standardized general anaesthesia included diazepam as premedicant, thiopentone, enflurane, N2O, fentanyl and vecuronium. Venous plasma concentrations of noradrenaline, adrenaline, growth hormone, vasopressin, and cortisol were assayed at various times before, during and after surgery. Clonidine attenuated the sympathoadrenal response; arterial blood pressure and heart rate increases in association with intubation were lower in clonidine-premedicated patients. Noradrenaline levels were lower throughout and 3 h after surgery in the clonidine group (P less than 0.05). Adrenaline levels were lower in this group 2 min after intubation (P less than 0.05). Growth hormone, vasopressin and cortisol plasma levels were increased at the end of and after surgery, with no differences between the groups. In spite of the effect on sympathoadrenal response, clonidine did not have any significant additive anxiolytic effect. Statistically significant differences were not found as to need for postoperative analgesics.