The performance of the Hitachi HME-20 pulse and blood-pressure (BP) monitor in comparison with direct intra-arterial BP recording and electrocardiographic monitoring is described. Highly significant (p<0·001) correlations were found between intra-arterial systolic and diastolic pressures and pressures recorded by the Hitachi monitor. Similarly, the electrocardiographically computed heart-rate, and that given by the Hitachi monitor were significantly correlated (p150 mmHg. These results are comparable to more expensive pulse and blood-pressure monitors. We conclude that the instrument can reproduce a satisfactory estimate of heart-rate and blood-pressure and may be of particular use when a change of blood-pressure is of prime importance, rather than an absolute measurement.