Abstract The effective charge content of the pericellular matrix of chondrocytes has been determined while the matrix is being synthesized by cells grown in culture for several weeks. The data were compared with estimates determined by chemical analysis. When measurements were performed after digestion of the matrix with papain, there was close agreement between results obtained from both techniques for proteoglycans synthesized by chondrocytes from nasal septum (a non-articular cartilage). By contrast, no such agreement was observed for proteoglycans synthesized by chondrocytes from articular cartilage, even after solubilization of the matrix with papain. While the charge calculated from chemical analysis showed a constant increase with time in culture, that measured by colloid titration showed a cyclical pattern, with maximal values occurring on days 7 and 24 of culture and a minimal value on day 14. This inability to detect all negative groups present in the matrix synthesized by articular chondrocytes would suggest the involvement of these groups in electrostatic interactions. Partial characterization of proteins synthesized by the pericellular matrix indicates that the decrease in charge content observed on day 14 could not be attributed to proteins of a particular molecular mass but possibly to an increase in the total amount of protein present It is concluded that the marked difference in the availability of negative groups between chondrocytes cultured from articular and non-articular cartilages may reflect differences in the interaction of these negative groups with matrix components; these differences would lead to the distinct structural organization of these two cartilaginous tissues which possess different mechanical functions.