High molecular mass-chondroitin sulfate was characterized for M(r), charge density and constituent disaccharides. This glycosaminoglycan was depolymerized by a controlled free-radical process mediated by hydrogen peroxide in the absence or presence of cupric or ferrous ions. Hydrogen peroxide depolymerizes chondroitin sulfate, and the velocity of the reaction increases in the presence of cupric ions and, further, of ferrous ions. Different low molecular mass-chondroitin sulfate fractions were produced and analyzed by high-performance size-exclusion chromatography and polyacrylamide-gel electrophoresis. This last technique strongly supports the hypothesis that the free-radical process proceeds by the destruction of disaccharide units. The treatment of free-radical chondroitin sulfate samples with chondroitinase ABC and testicular hyaluronidase results in a lower capacity of these enzymes to degrade these glycosaminoglycan derivatives with respect to the natural sample. This was confirmed by polyacrylamide-gel electrophoresis and by the time-courses of enzymatic treatment evaluated by spectrophotometric technique (for treatment with chondroitin ABC lyase).