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This paper presents an experimental investigation of the effects of air injection on the rotating stall instability in a low speed axial compressor. Two experiments concerning air injection were tried. The first experiment used a continuous forcing perpendicular to the flow in the same or opposite direction of the tip velocity. The results show a dramatic difference between the two directions, with opposite direction forcing causing a significant increase in performance, and same direction forcing causing a significant decrease in performance. This result contradicts the Emmons stall propagation model. The second experiment investigated the differences with respect to different frequencies of air injection, with the injector pointed at the fan, parallel to the flow. We found that the change in the compressor characteristic in the unstalled region was highly dependent upon the forcing frequency with the maximum change occurring near the frequency of stall.