To understand the molecular events underlying rheological vitreous changes, age-related changes in the molecular properties of bovine and human vitreous collagen were monitored by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The adult bovine vitreous showed an increase in the highmolecular-weight components of the collagen compared with the young samples. In addition, the apparent molecular size of theα-chain of the adult type II collagen was slightly larger than that of the young samples. The same tendency also was observed in human vitreous. The increase of high-molecular-weight components of the vitreous collagen could be attributed to intermolecular cross-links of the peptide chains.