The sedimentation of erythrocytes has been measured using the standard Westergren method inside and outside a homogeneous static magnetic field. The magnetic field of 6.3 T in the vertical direction greatly enhanced the sedimentation of erythrocytes in their own plasma compared with that in saline solution. The maximum slopes of sedimentation curves increased and the time requaired at the maximum slope decreased in plasma. The effect in plasma was too large to originate only from cell orientation.