A comparative study was made of 33 explanted intraocular lenses (IOL) by stereomicroscope, light microscope, phase-contrast microscope, scanning electron microscope and transmission electron microscope. The materials of the extracted lenses were polymethylmethacrylate (PMMA), silicone, polyhydroxyethylmethacrylate (PHEMA) and coated PMMA. The implanted period varied between 3 days and 88 months. An ultrathin membrane-like structure composed of fine, granular material, 0.01 to 0.08 microns thick, that covered the entire explanted IOL surface was observed regardless of the implant period and kind of IOL. The structure was determined to be a layer of adsorbed protein since it showed a positive reaction to protein stainings such as Ponceau 3R, nigrosine or ruthenium red. No membranous structure or cellular deposit could be seen on the surface of the unused PMMA IOL which served as a control.