Ultrasonic Doppler flowmeters can simultaneously obtain spatial and velocity distribution patterns of flow in a blood vessel. The factors fixing spatial and velocity resolution, however, must be determined if optimum utilization is to be realized. The parameters influencing spatial resolution have been described in the literature, but velocity resolution has received relatively little attention. This paper demonstrates analytically how optimum velocity resolution can be derived with a simple mathematical model and presents experimental data to verify theory. In addition, a ’’resolution product’’ is offered which characterizes pulsed Doppler flowmeters. This product shows explicitly the necessary compromise between position and velocity resolution for a given instrument.Subject Classification: [43]28.60, [43]28.20; [43]80.70; [43]35.80.