Labetalol, an alpha- and beta-adrenergic receptor-blocking agent, was studied as a hypotensive agent during halothane (mostly 0.5 vol.%)-N2O-fentanyl-d-tubocurarine anaesthesia with a head-up tilt of 5 degrees in 41 patients undergoing middle ear microsurgery. After the mean initial dose of 0.3 mg/kg, the mean need for labetalol ranged from 0.05 to 0.07 mg/kg at 30 +/- 5-min intervals. The mean duration of the hypotensive period was 102 min. During the hypotension, the average mean arterial pressure ranged from 59 to 62 mmHg (7.9-8.3 kPa) and the mean heart rate from 61 to 66 b.p.m. After labetalol the maximum cardiac output decrease was 7%. Before labetalol the mean PaO2 value was 158 mmHg (21.1 kPa) and during hypotension it ranged from 145 to 149 mmHg (19.3-19.9 kPa) when FiO2 was 40%. The only peroperative side effects were ECG changes (middle junctional rhythm and sinus bradycardia) which occurred in 10% of the patients. The mean value for the degree of haemostasis rated by the otologist on a visual analogue scale between poor (0 mm) and excellent (100 mm) was 91 mm. The patients were able to open their eyes and to give their names 8-9 min after the end of anaesthesia. After extubation the patients were normotensive and there were no clinically significant changes in the cardiovascular parameters during the 4-h recovery room period. Acid-base status showed slight metabolic acidosis. The most common postoperative side effects were nausea only and nausea + vomiting, which occurred in 39% and 20% of the patients, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)