Chondrocytes isolated from the caudal and cephalic ends of the sterna of embryonic chicks were cultured in collagen gels. Differences were found, histochemically, between the proteoglycans produced by the "caudal" and "cephalic" cultures and with length of time in culture. The cultures were labelled with [14C]galactose and [35S]sulphate at 7 and 21 days in culture and labelled compounds from media, and cell and matrix extracts analysed with Sepharose CL-2B. A large aggrecan-like proteoglycan was detected in the media with some aggregated proteoglycans found in the cell extracts even under the dissociating conditions used. One group of 14C-labelled compounds, found in the cell and matrix extracts, was equivalent in size to chick aggrecan core protein. Smaller proteoglycans and glycoprotein glycans were present. The types and proportions of these proteoglycans varied between the two cell types demonstrating biosynthetic commitment.