Numerical and experimental investigations were carried out to improve the knowledge of the flow field in solid/liquid suspensions in agitated vessels and to examine the ability of the commercial CFD, code CFX 4.2, for this application. The numerical results were compared with our own experimental results of time resolved Laser-Doppler-Velocimeter (LDV) and power input measurements with particle concentrations of up to 15 percent of the volume. To perform LDV measurements within the solid/liquid flow the refractive index matching method was used. Results of the CFD simulation show the necessity to use high grid resolution, the k-epsilon turbulence model and an advanced discretization scheme to achieve a grid-independent solution. Simplifications of the grid geometry were shown to be an acceptable way to minimize the time required for calculation. The comparison of experimental and numerical results shows good agreement for velocities and power input in the single- and in all two-phase flow cases. Good agreement with regard to the kinetic energy k is also apparent, except in the region near the stirrer blades, where local maxima are underestimated by the simulation.