The contrast effects that occur in the orientation-dependent patterns obtained with the scanning electron microscope by collecting secondary emitted and/or primary back-scattered electrons have been explained in terms of the electron channelling mechanism. Markedly different contrast effects occurred when such patterns were obtained by using the specimen current electrons. In the present work, the latter patterns have been investigated, and it is shown that these contrast effects arise from the channelling of electrons plus signal differentiating effects associated with the additional amplification required.Such differentiation can be both advantageous and disadvantageous as far as electron channelling patterns are concerned. It has been found convenient in practice to use an amplifier that does not differentiate the signal, and to incorporate differentiating circuits that can be either switched in or shorted out.