The research program of Unit 2.1B, Real-Time Ultrasonic Flow Imaging, of the National Science Foundation/Engineering Research Center (NSF/ERC) is described. The objective of the unit's research is to develop effective techniques and prototype instrumentation for angle-independent visualization of blood flow and tissue motion in real-time ultrasound. An offline evaluation of algorithms for tracking speckle patterns was completed. Quantitative studies indicate that a sum-absolute-difference (SAD) algorithm tracks speckle patterns as accurately as normalized cross correlation, yet requires only one-eighth as many operations per pixel. A scheme for color encoding motion vectors for two-dimensional display was developed and applied to clinical blood flow data with favorable results. A prototype angle-independent flow imager based on the SAD algorithm is under development.