Detailed accurate measurements of velocities, directions, and fluctuation intensities were performed with a newly developed laser velocimeter in the internal flow field of a radial discharge impeller, running at tip speeds up to 400 m/s. Relative flow distributions are presented in five measurement areas from inducer inlet to impeller discharge. The impeller flow pattern, which coincides largely with potential-theory calculations in the axial inducer, becomes more and more reversed when the flow separates from the blade suction side, developing a rapidly increasing wake in the radial impeller. The observed secondary flow pattern and effects of channel curvature and system rotation on turbulence structure are discussed with respect to separation onset and jet/wake interaction.