Abstract: Doppler ultrasound is an extremely valuable technique for detecting and measuring blood flow and other movements within the body, however it still suffers from a number of limitations. Three of these limitations, together with possible solutions will be discussed. 1) The vector problem. All conventional Doppler ultrasound instruments measure the component of velocity towards or away from the transducer. In many situations this is not a problem, but where complex flow patterns are present this may give misleading information. Solutions to this limitation include vector Doppler systems, transverse Doppler systems, speckle tracking systems and multiple beam methods. 2) The frame rate problem. In general Doppler frame rates are much lower than imaging frame rates because in order to get a reliable estimate of velocity it is necessary to sample each region of interest several (often between 8 and 16) times, whereas to generate a pulse-echo image it is only necessary to sample once. One potential solution to this is to use synthetic aperture techniques which greatly speed up image acquisition. 3) Axial resolution. The axial resolution of some Doppler systems is limited by the transmitted pulse length. A solution which has previously been applied to pulse echo systems is to use coded excitation. It now appears that a similar solution can be used for Doppler signals without introducing the serious artifacts that might be anticipated.