Solutions made by homogenization of vitreous humor exhibit anomalous viscosity at low shear rates due to interaction between hyaluronic acid and a hydroxyproline-containing material similar to collagen. The latter can be removed by filtration or centrifugation to give a solution whose viscosity is due to hyaluronic acid. On concentration the viscosity of the latter remains independent of shear rate and it is concluded that hyaluronic acid in the vitreous humor is not greatly asymmetric. There is no evidence that the soluble protein of vitreous humor contributes to the viscosity. Hyaluronic acid in vitreous humor is not in chemical combination with protein. The interaction between the hyaluronic acid and the collagen-like material is ascribed to weak, coulombic forces.