To evaluate the accuracy of measurements of the velocities and timing of blood flow and of tissue motion, we tested four commercially available ultrasound systems. Pulsed wave, continuous wave and tissue Doppler recordings acquired across a range of angles of insonation were compared against a calibrated Doppler string phantom. Temporal delays were measured from the onset of the simulated electrocardiogram to the start of each Doppler signal. Across all modalities and angles, the mean errors of measurements of velocity using the four systems were 0.2%, 1.7%, 6.0% and 3.1%. The largest errors occurred using tissue Doppler at 5 cm/s (mean overestimation: 5.8%, range: +1.1%-12.5%). Mean delays in displaying the onset of flow were -3, 6, 11 and -16 ms. All differences between machines were statistically significant. The accuracy of high-end ultrasound systems for measuring velocities is better than in earlier reports, but the reporting of routine testing against standard phantoms should be mandatory.