The very viscous solution of a special fraction of Na-hyaluronate, Healon ® was used to replace the aqueous humor in rabbits. The intraocular pressure, corneal thickness and endothelial cell count after Na-hyaluronate injection were not significantly different than after replacing the aqueous humor with balanced salt solution. The same viscous Na-hyaluronate solution was also shown to protect the corneal endothelium from mechanical damage caused by contact with methacrylate surfaces. Corneal endothelial cell counts in histological preparations and in scanning electron micrographs clearly showed that placing the viscous Na-hyaluronate solution between the methacrylate surface and the corneal endothelium prevented the mechanical damage.