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A new prototype system for the noninvasive measurement of instantaneous blood pressure (BP) in the human radial artery has been developed. The system is based on the volume-compensation method, but several components were newly designed, namely, a disk-type cuff for local pressurization and a nozzle-flapper-type electro-pneumatic converter (EPC) for the cuff-pressure control. Results of experiments indicated that, using the disk-type cuff, the radial artery could be completely compressed, and the newly devised EPC had sufficient frequency response for BP measurement in humans. It was also found that the prototype system comprising these components was capable of noninvasively measuring instantaneous BP in the human radial artery, not only under rest conditions but also in a stressful condition, such as during the cold pressor test. In conclusion, the newly developed local pressurization technique appears promising as a useful and helpful means for instantaneous BP monitoring over longer periods of time than have previously been possible. Using this method, it is possible to construct an instrument that is more compact and more comfortable for the subject to use than a conventional commercial instrument. Finally, it has been reported that it may be possible to monitor cardiac output continuously by BP waveform analysis. Thus, continuous cardiac output monitoring might be another potential and important application of the newly designed instrument.