Acanthamoeba keratitis has frequently been associated with contact lens use. In this study, contaminated hydrogel contact lenses of patients were subjected to disinfection by thermal hydrogen peroxide and chemical (quaternary ammonium) systems. New hydrogel contact lenses contaminated by incubation on Acanthamoeba polyphaga plates were similarly subjected to the disinfection systems described above. Thermal disinfection was universally effective in eradicating acanthamoeba, whereas hydrogen peroxide and quaternary ammonium disinfection were ineffective. Scanning electron microscope photomicrographs suggest that acanthamoeba may adhere to surfaces of hydrogel contact lenses. These findings have significant implications for soft contact lens users.