A dependent Bloch wave theory for inelastic scattering is adapted to predict backscattered electron (BSE) contrast from perfect crystals. This is correlated with 300 keV data from a number of zone axes from spinal, chromia, silicon, aluminium and gallium arsenide. This theory is shown to supersede an independent Bloch wave theory for BSE contrast which is incapable of accounting for asymmetry across polar axes. Orientation dependence of thermal dechanneling of fast electrons is shown to be important. The BSE scattering potential is shown to approximate to a delta function scaled by the atomic number squared on each atom. 25 refs., 1 tab., 9 figs.