In a double-blind, randomized, placebo-controlled study, 41 patients received clonidine 3 micrograms kg-1 or placebo at induction of isoflurane and nitrous oxide in oxygen anaesthesia. Metoprolol was also given to achieve a systolic arterial pressure of 80 mm Hg. Requirements for metoprolol were significantly less in the clonidine group (P < 0.00035), with no significant difference in mean arterial pressures over time. It would appear that clonidine is an i.v. hypotensive agent worthy of consideration, but data during the recovery period are required to comment further on the safety of this technique.