Aortic glycosaminoglycans were separated into fractions of increasing molecular weights containing heparan sulfate or chondroitin 4/6-sulfate + dermatan sulfate. When these fractions were added to plasma low density lipoproteins (LDL) in the presence of Ca2+, only chondroitin 4/6 sulfate + dermatan sulfate of high relative molecular weight produced turbidity. Treatment with testicular hyaluronidase abolished totally the formation of insoluble complex. When these glycosaminoglycans were applied to LDL-affinity columns in the presence of Ca2+, higher NaCl concentrations were necessary for the elution of the high relative molecular weight chondroitin sulfate. Heparan sulfate fractions did not produce turbidity when added to LDL solutions and were eluted from LDL-affinity columns at low NaCl concentrations. All these results suggest that besides the structure (or charge density), the molecular weight of the chondroitin sulfate chains is a relevant factor for the binding of this compound to LDL.