High-quality photographic recording of X-ray diffraction data from the hard alpha-keratins has mainly been limited to that from porcupine quill. Earlier diffraction patterns of hair have shown very few reflections. In the present study, extensive sets of high-quality data have been obtained using a synchrotron source and an image plate detector, revealing information about the internal structure, both axial and lateral. The diffraction patterns of hair from six different baboons have been examined. The meridional axial diffraction data reveal evidence of the superposition of three and possibly four separate lattices. Despite considerable overlapping, sufficient reflections unique to each lattice have been observed. These lattices comprise an infinite one of 46.76 nm, together with finite lattices of 19.67, 27.20 and 7.27 nm. These patterns reveal information regarding the fibrillar structure of the hair fibres, namely that it consists basically of cylindrical fibrils arranged in a disordered lattice. The mean diameters of these cylinders have been determined, together with their average separation. There is also an indication of the presence of another set of cylinders of smaller diameter, possibly comprising the microfibrils of keratin.