Abstract: A method and apparatus for distinguishing between solid masses and fluid-filled cysts by using an ultrasonic transducer to transmit a plurality of ultrasonic signals into a target lesion within a human body and for receiving a plurality of reflected signals therefrom. At least one of the plurality of transmitting signals should be of sufficient intensity to initiate movement of any fluid located within the target lesion. A plurality of reflected ultrasonic signals are received from the target lesion and a comparison of differences between individual ones of the plurality of reflected signals is made to detect the presence or absence of fluid movement within the target lesion. Then a determination is made as to whether the target lesion is a fluid-filled cyst or a solid mass based upon the presence or absence of fluid within the target lesion.