It is now generally accepted that Persistent Slip Bands which form during fatigue of single crystals quickly propagate through the bulk of the specimen; early work which suggested that PSB's were a surface phenomenon was confined to modes of testing in which the strain amplitude decreases with depth below the surface. In polycrystals the situation is less clear and there seems to be a general belief that PSB's are confined to the surface grains. This paper presents a preliminary result which suggests that even in polycrystalline specimens, persistent slip may be a bulk phenomenon.