A histologic study of surgically removed rheumatoid metatarsal and metacarpal heads showed that, at this late stage of the disease, the changes in residual cartilage are mainly reparative. An outstanding one is the formation of a new surface under dead cartilage, analogous to the replacement of a snake's skin. Dead cartilage has to be eroded in toto. When live cartilage is exposed to vascular tissue, the chondrocytes take part in the involutionary process. Chondrocytes also appear to initiate the process described as pannus. Deformities are often produced by flask-shaped defects showing severe marginal osteitis. Active erosion of the surface by synovial adhesions has probably been overemphasized in the literature.