Different proteoglycans (PGs) were isolated from pig aorta for aggregation studies with hyaluronic acid and human low-density lipoproteins (LDL). Extraction of the intima-media with 4M-guanidinium chloride and digestion of the residue with collagenase solubilized 91% of aortic hexuronic acid content. From the guanidinium chloride extract two PGs were isolated by ion-exchange and gel-permeation chromatography: proteochondroitin sulphate (PGI) with a protein-core apparent Mr of 250 000 and proteodermatan-chondroitin sulphate (PGII) with a protein-core apparent Mr of 55 000. Only PGI forms high-Mr aggregates with hyaluronic acid. From the collagenase digest two other PGs were isolated: proteoheparan sulphate and proteochondroitin sulphate (PGIII and PGIV respectively). PGIV had a smaller hydrodynamic size than PGI. PGI and PGII formed insoluble complexes with human LDL in the presence of Ca2+. PGIII or PGIV did not form precipitates with the LDL. PGI and PGII, but neither PGIII nor PGIV, were bound to LDL-Sepharose. The main peaks of PGI and PGII were eluted from LDL-Sepharose with 60 mM- and 90 mM-NaCl respectively. The results indicate that aortic PGs have different interacting potentials with lipoproteins, depending on their Mr and their glycosaminoglycan composition.