The articulating surfaces of bones which ossify in mesenchyme, like the mandible, are covered by a layer of dense, fibrous tissue. The purpose of the present study was to examine the structure of the mandibular condyle in the monkey. Young Rhesus monkeys (Macaca mulatta) were perfused with glutaraldehyde-paraformaldehyde. Small pieces of the condyles were dissected out, demineralized in 0.5 M EDTA and processed for light microscopy and electron microscopy. The mandibular condyle was covered by an avascular tissue, extending from the surface to the underlying bone. The tissue could be divided into three zones. The zone facing the articular cavity was about 50/zm wide and consisted of a dense, fibrous tissue. Layers of collagen fibers, I~SS ttm wide and parallel with the articular surface, but oriented at angles to each other, were seen. Between the collagen fibers fibroblast-like cells were noted. The second zone was also approximately 50/zm wide and rich in cells. The cells were ovoid or fiat and had a dark staining cytoplasm with some mitochondria and a well developed rough-surfaced endoplasmic reticulum. The third zone was about 150,um wide and here the cells were larger and located in lacunae. An increase in the size of cells and lacunae was seen approaching the bone. This zone showed hyaline cartilage undergoing maturation. Closer to the bone, degeneration of the chondrocytes was noted. In the underlying bone, soft tissue with several chondroclasts resorbing the hypertrophic cartilage were seen, alternating with areas where bone formation was occurring, partly on the top of cartilage remnants. The observations confirm that in the growing condyle there is an articular part as well as a growth zone, and that the cells in the cell-rich zone serve as precursors for the hyaline cartilage cells in the growth zone, and possibly as a cell reservoir for the articular part as well.