To produce a blood-free field for middle ear surgery performed with the operating microscope, the arterial systolic pressure was reduced to less than 50 mm Hg in 700 patients by means of thiopentone-halothane-nitrous oxide in oxygen anaesthesia together with pentolinium tartrate. In 84% the results were excellent, in 12% moderately good and they were poor in 4%. There were more unsatisfactory results in males (22.8%) than in females (11.4%). In spite of the arterial pressure being reduced to very low values in many instances, there was no mortality or morbidity which could be ascribed to the technique.