Relates to hydrophones, employing piezoelectric sensor elements, designed to measure the pulsed and continuous-wave ultrasonic fields generated by ultrasonic medical equipment operating in the frequency range 0.5 MHz to 15 MHz. Covers the design and performance requirements of standard hydrophones and the data required to specify their characteristics, and defines a standard method for the measurement of the sensitivity of such hydrophones. Defines the performance characteristics that are required of hydrophones intended for use in a specified range of applications over the frequency band from 0.5 MHz to 15 MHz, particularly those associated with the measurement of pulsed and continuous-wave ultrasonic fields used in medical diagnosis. Establishes a scheme for the specification of the performance of these hydrophones. Describes a standardized procedure for their calibration.