We studied the effects of a single i.v. dose of dexmedetomidine, a highly selective and specific alpha 2 adrenoceptor agonist, on intraocular pressure (IOP), haemodynamic and sympathoadrenal responses to laryngoscopy and tracheal intubation, and on anaesthetic requirements in ophthalmic surgery. Thirty ASA I-II patients undergoing cataract surgery were allocated randomly to receive either dexmedetomidine 0.6 microgram kg-1 or saline placebo i.v. 10 min before induction of anaesthesia in a double-blind design. After dexmedetomidine there was a 34% (95% confidence interval (CI) 27-43%) reduction in IOP (P less than 0.001) and 62% (CI 57-68%) decrease in plasma noradrenaline concentrations (P less than 0.001). After intubation, maximum heart rate was 18% (CI 3-33%, P = 0.036) and the maximum IOP 27% (CI 11-43%, P = 0.005) less in the dexmedetomidine group compared with the patients treated with placebo. Within 10 min after intubation, maximum systolic and diastolic arterial pressures were also significantly (P = 0.013 and P = 0.020) smaller in the dexmedetomidine group. The induction dose of thiopentone was smaller (23% (CI 20-26%) P = 0.012), and the use of isoflurane or fentanyl supplements during anaesthesia was less frequent in the dexmedetomidine group. The patients premedicated with dexmedetomidine recovered faster from anaesthesia (P = 0.042). These results suggest that dexmedetomidine may be a useful anaesthetic adjunct in ophthalmic surgery.