A topographical study of the articular surface of 21 femoral heads removed for surgery of osteoarthrosis was made using the scanning electron microscope. Sections of degenerate cartilage were pretreated with H2O2 and trypsin to reveal the collagenous framework. Torn and frayed collagen bundles were evident on all the specimens studied, the length of these bundles varying from 20 to 150 micron. The frequency of the bundles over the degenerate fibrous areas varied considerably, and bundle sizes ranged from 20 to 70 micron. The topography of a single femoral head removed from a rheumatoid arthritic was very much smoother, with torn fibre ends ruptured at the same level. Although the exposed bone was considerably "smoother" than the residual fibrocartilage, ruptured osteons and trabeculae revealed large voids in the surface which would presumably alter the lubrication and fluid flow characteristics of the functioning joint. The effects of these changes on joint tension and lubrication are discussed.