The core protein of high buoyant density proteoglycans synthesized by chondrocytes in stage 24 chick limb bud mesenchymal cell cultures was cleaved with cyanogen bromide to produce 17 resolvable peptides on sodium dodecyl sulfate-polyacrylamide slab gels. Of these peptides, 10 appear to originate from the chondroitin sulfate-rich region, 2 appear to be derived from the keratan sulfate-rich region, and 5 seem to be derived from the hyaluronic acid-binding region. The peptides from the chondroitin sulfate-rich region are almost all large (200 to 64 kDa). In contrast, the peptides from the keratan sulfate-rich and hyaluronic acid-binding regions are relatively small (47 to 12 kDa). One peptide from the hyaluronic acid-binding region appears to contain mannose-rich N-linked oligosaccharides as inferred from its observed binding by concanavalin A. A different hyaluronic acid-binding region peptide and one of the keratan sulfate-rich peptides were shown to contain disulfide bonds and therefore may be involved in contributing to the tertiary structure of the hyaluronic acid-binding region. Based on these observations, a map of the chick chondrocyte proteoglycan core protein has been constructed.