The power in the core of a bent multimode slab is calculated on the basis of ray theory as a function of the angle round the bend, and as a function of the bend radius of curvature. The effect of cladding thickness is also taken into account. Measurement of the power in the core of a bent multimode fibre supports the validity of the two dimensional slab model used, and also the mechanism of refracting rays being responsible for the power transfer to and from the core of such bent fibres.