X-ray diffraction studies of hard alpha-keratin have led to a proposed model for the lateral arrangement of molecules within the keratin fibrils of tissues such as hair, nail and claw. Using low-angle synchrotron radiation to examine human scalp hair we have obtained discrete equatorial diffraction maxima which have not been reported previously. These reflections can be divided into three subsets. The first of these reveals the information that the hair fibres consist basically of cylindrical fibrils arranged in a disordered lattice. The mean diameters of these cylinders have been determined, together with their average separation. The diameters of the protofibrils have been determined from the second set. The third set, a set of diffuse arcs, index onto a spacing which is characteristic of the disordered components of the matrix.