In this paper, axial thrust problems of multistage pumps are presented. The entire investigation has been focused on the pump design concept having all impellers in series (facing in one direction) and is valid for barrel casing type as well as for segmental type. The major part of the investigation has been experimental on one stage testing arrangement, using also Laser Doppler Anemometry (LDA) for determination of fluid rotation in the impeller side chamber. Numerical flow analysis (NFA) has been applied for some flow variants in order to verify whether a numerical approach could simulate the test results. The phenomenon of fluid rotation in side chambers and its effect on impeller hydraulic axial thrust have been determined for different leakage flow regimes. The influence of increased wear ring radial clearance on axial thrust has been analyzed together with the solutions for pump hydraulic axial thrust reduction.