Mean blood velocity (Vmean) is needed for calculating blood flow and possibly the pressure gradient across the ductus venosus. Interference from low velocities from neighbouring vessels makes the direct Doppler measurement of Vmean unreliable. Therefore, it is suggested that Vmean can be derived more reliably from the maximum velocity (Vmax) once the velocity profile, expressed as the ratio Vmean/Vmax, is known. To determine this ratio, ultrasound was performed in 10 fetal sheep during acute experiments under general anaesthesia to ensure good recording control and optimal insonation. Based on 33 Doppler measurements at the ductus venosus inlet, the ratio Vmean/Vmax was determined to be 0.69 (SD +/- 0.07) regardless of Vmax, pulsatility index, vessel diameter, or angle of insonation. These results confirm the previous prediction based on a computational model that the velocity profile is partially blunted. The equation Vmean = 0.7Vmax is recommended for determining Vmean in the ductus venosus.