Abstract: To improve the accuracy of blood pressure measurement by utilizing the Korotkoff noises, the frequency spectrum of the Korotkoff noises is analyzed, either by a plurality of filters (16, 17, 18; FIG. 1) or by a Fast Fourier Transform (FFT) system (54, 55; FIG. 2). If a plurality of filters are used (FIG. 1), which may be analog or digital, then the output amplitudes are rectified (19, 20, 21) and quotients are formed. If the quotients have a predetermined relationship, as determined by a discriminator (27, 28), a control logic provides output signals to a manometer (31) to indicate, respectively, systolic and diastolic blood pressure. For Fast Fourier Transform, a microprocessor can be used which, simultaneously, can provide clock sources to digitize output from the microphone coupled to the cuff of the blood pressure measuring instrument.