Multipotential hemopoietic progenitor cells (FDCP-mix) proliferate in culture medium supplemented with horse serum. When transferred to a medium without serum, cells do not proliferate and enter a quiescent state. Both proliferative and quiescent cells synthesize only chondroitin sulfate proteoglycan (CS-PG) which is associated to the cell membrane. Incorporation of 35SO4 into CS-PG was 4-fold higher in quiescent than in proliferative cells. Flow cytometric studies using monoclonal antibodies which recognize the core protein or the CS chains, showed that the increased uptake of sulfate was not the consequence of an increase in the abundance of CS-PG. Further characterization demonstrated that CS-PG isolated from quiescent cells exhibited a slightly higher hydrodynamic size than CS-PG from proliferative cells. However, the glycosaminoglycan chains from PG derived from proliferative and quiescent cells have the same hydrodynamic size. Through ion-exchange chromatography we observed that the mean charge density of PG from quiescent cells was higher than in proliferative cells, suggesting a higher sulfation degree from PG synthesized by quiescent cells. This was confirmed by flow cytometric studies using monoclonal antibody 2B6, which recognizes the unsaturated terminal disaccharide of chondroitin-4-O-sulfate.