This study investigated the accuracy of phase contrast MRI in blood flow measurements; both in vitro and in vivo studies were carried out. Five normal volunteers (3 women and 2 men, age range: 24 to 30 years) were examined with MR angiography (MRA) and a flow measurement sequence. A 2D phase contrast sequence, with retrospective cardiac gating was also acquired with the following imaging parameters: TR/TE/FA (26/9.3/20 degrees ), field of view 150 mm, matrix 96 x 128; 4 averages. VENC value (cm/s) was chosen according to the examined region. The total acquisition time ranged 3 min 25 sec to 4 min 38 sec. The sequences were acquired on a plane perpendicular to the vessel direction, using MIP-reconstructed MRA images as a scout view. The results are the same as those obtained with other techniques, in the common carotid artery (Vmax = 70.7 cm/s; Vmin = 18.8 cm/sec; flow = 348 ml/min), internal carotid artery (Vmax -54.4 cm/sec; Vmin = 18 cm/sec; flow = 236 ml/min) and vertebral artery (Vmax = 51.7 cm/sec; Vmin = 17.5 cm/sec). The resistance index could always be calculated and exceeded 0.7 in all cases. In conclusion, MRA is an accurate technique for blood flow measurements, in particular with cardiac gating, which permits measurement optimization according to the different cardiac cycles.