The effects of three different doses (0.5, 1.0 and 1.5 micrograms/kg) of dexmedetomidine, a novel alpha 2-adrenoceptor agonist, on vigilance, anaesthetic requirements, haemodynamics, and plasma catecholamine levels were investigated in a double-blind placebo-controlled study in 20 healthy (ASA physical status I-II) women scheduled for uterine dilatation and curettage (UD&C). The drug was administered intramuscularly 60 min before induction of anaesthesia with thiopentone, N2O/O2 (70/30%) and thiopentone was used for maintenance. There were no significant differences between the groups in thiopentone requirements, plasma adrenaline concentrations, or subjective or objective assessment of sedation before anaesthesia and UD&C. Blood pressure, heart rate, and plasma noradrenaline levels were reduced after dexmedetomidine, with three patients receiving atropine for excessive bradycardia (less than 45 beats min-1). The haemodynamic as well as the sedative effects of dexmedetomidine after surgery lasted until the end of the observation period, 4 h after the injection of the drug, indicating that intramuscular administration of this premedication agent may result in a longer than optimal duration of pharmacological actions in connection with short surgical procedures.