Use of the Doppler principle with an ultrasound flowmeter provided a method of detecting fat emboli during total hip replacement. A measure of the quantity of fat emboli and when the embolism occurs during the operative procedure is possible with this method. By the use of a suction catheter inserted in the intramedullary canal or the placement of large drill holes in the lateral cortex of the femur the amount of fat released into the venous circulation can be reduced. Although no definite signature could be obtained for the audible "chirps" by energy density spectrum analysis the observer could readily distinguish these chirps from the burbling noise produced by air emboli. Ultrasound is an easy, noninvasive and reliable technique for detecting fat emboli during total hip replacement.