Detailed flow measurements made in the casing boundary layer of a two-stage transonic fan are summarized. These measurements were taken at stations upstream of the fan, between all blade rows, and downstream of the last blade row. At the design tip speed (429 m/sec) the fan achieved a peak efficiency of 0.846 at a pressure ratio of 2.471. The boundary layer data were obtained at three weight flows at the design speed: one near choke flow, one near peak efficiency, and one near stall. The data presented show steep axial velocity profiles at the stator exits were not as steep as those at the rotor exits. The data also show overturning of the flow at the tip at the stator exits. The effect of mixing is shown by the redistribution of the first-stage rotor-exit total temperature profile as is passes through the following stator.