In the design of cascade blading for compressors and turbines it is often assumed that the maximum efficiency will be attained at the maximum loading that just avoids separation and critical Mach number effects. In a turbine, the overall pressure gradient is favourable so that it should be possible to achieve very high loadings and yet avoid separation. The question then arises as to whether or not such high loadings would produce a high efficiency. The present note suggests that in fact there is an optimum loading, beyond which there would be no improvement in efficiency even though separation and critical Mach number effects were avoided.