Arterial smooth muscle cells cultured from rat aorta were labelled with sodium [35S]-sulfate in combination with either [3H]glucosamine or [3H]mannose. The newly synthesized hyaluronate and sulfated proteoglycans obtained from the growth medium (M-PG) and extracted from the cell layer (C-PG) with 4M guanidinium chloride in the presence of proteinase inhibitors were purified by sequential fractionation on Sepharose 4B CL, equilibrium density gradient centrifugation and ion exchange chromatography under dissociative conditions. Gel filtration of M-PG resulted in the separation of free hyaluronate and two size classes of [35S]-proteoglycan populations eluted at Kav 0.15 (fraction M-A) and 0.48 (fraction M-B). On further fractionation M-A dissociated into hyaluronate (Mr 1.6 X 10(6)) and a proteoglycan monomer (M-PG A, Mr 180 000), which contained chondroitin 4-sulfate (Mr 21 000) as the main glycosaminoglycan moiety. The proteoglycan isolated from M-B (M-PG B) was identified as a proteoglycan monomer (Mr 200 000) containing mainly chondroitin sulfate/dermatan sulfate hybrid side chains (Mr 34 000). [3H]Mannose labelling and binding to ConA Sepharose of both M-PG A and B indicated the presence of oligosaccharides of the glycoprotein type. An analogous fractionation of proteoglycans associated with the cell layer yielded two hyaluronate-proteoglycan complexes (C- PreA and C-A). The proteoglycan monomers of these complexes (C-PG PreA and C-PG A) had Mr values of 420 000 and 130 000. A non-complexed proteoglycan monomer C-PG B (Mr 90 000) was also found. All cell layer bound proteoglycans had glycosaminoglycan side chains with Mr approximately 36 000 but the predominant glycosaminoglycan component was either heparan sulfate, chondroitin sulfate or dermatan sulfate. All cell layer bound proteoglycans contained [3H]mannose radioactivity, about 15% of which was bound to ConA Sepharose.