Eight cows underwent Doppler sonographic examinations of the milk vein and musculophrenic vein from 9 days prepartum to 300 days postpartum. A 7.5-MHz linear transducer was used to determine the inner diameter of the veins and blood flow velocities and volumes on the left side in standing, non-sedated animals. Cows were weighed and milk yield measured at all examination times. The milk vein appeared as a vessel with an inner diameter of 2.01-2.30 cm immediately beneath the skin. The maximum blood flow velocity ranged from 23.84 to 35.76 cm/s before parturition, increased markedly on the day of calving (day 0), peaked at 61.14 cm/s on day 1 and slowly decreased to 23.84 cm/s by day 300. The profiles of the minimum and mean maximum flow velocities and flow volume were similar. The musculophrenic vein had an inner diameter of 0.76-1.07 cm and its distance from the surface of the skin was 1.15-1.31 cm. The profiles of the blood flow variables were irregular and did not resemble those of the milk vein. The maximum blood flow velocity ranged from 87.35 to 114.41 cm/s, the minimum velocity from 5.47 to 7.60 cm/s, the mean maximum velocity from 48.55 to 78.74 cm/s and the blood flow volume from 1.02 to 2.44 l/min. The milk vein had a larger diameter (2.16 versus 0.90 cm; P<0.01), smaller maximum, minimum and mean maximum blood flow velocities (P<0.01) and a larger blood flow volume than the musculophrenic vein (P<0.01).