A two-camera PIV technique was used to obtain angle resolved velocity and turbulence data of the flow in a lab-scale stirred tank, equipped with a Rushton turbine. Two cases were investigated: a single-phase flow and a gas-liquid flow. In the former case, the classical radial jet flow pattern accompanied by two trailing vortices was observed. In the latter case, the velocity of the radial jet was reduced, and the vortices were diminished by the presence of the gas. Gas cavities clinging to the back of the impeller blades were observed. Both cases were also investigated with the use of three-dimensional transient CFD simulations. For the single-phase flow the simulations in the impeller region correspond very well with the experimental data. For the gas-liquid flow both the mean and fluctuating liquid velocities in the impeller region are well predicted. This is also the case for the mean radial gas velocities.