CELL membranes can be readily visualized in the electron microscope; but a rather special cell system is needed if one wishes to study their supposed role1,2 in morphogenesis. In the hair follicle we have been able to examine at high resolution a system which fulfils most of the electron microscopist's demands. It is small enough not to make the task of surveying it at high magnification too formidable and, in a geometrical sense, simple, in that the differentiating cells move away from the papilla in almost linear streams, preserving the order of their formation.