In state-of-the-art research of multiphase flows, numerical simulations are performed time-dependently and in three dimensions. For the validation of such simulations the availability of quantitative measurement data is crucial. In this study angle resolved and angle-averaged flowfields of the liquid in the vicinity of a Rushton impeller in a stirred tank were measured with the use of particle image velocimetry (PIV). Single-phase liquid flowfields were compared with flowfields of the liquid in an aerated stirred tank. The characteristic trailing vortices in the single-phase flow were observed. When the tank was aerated, the trailing vortices disappeared. Furthermore, the flowfield turned out to be less periodic than without gas. The measured liquid velocities in the impeller-swept region were 50% lower in the case where gas was present. The absolute liquid velocity fluctuations in the presence of gas were of the same order of magnitude as in the case without gas, but when scaled with the maximum radial velocity the relative velocity fluctuations were significantly larger than in the single-phase flow.