Acanthamoeba culbertsoni was used in this study inasmuch as its susceptibility to disinfection has not been examined. Although heat was found to be the most effective means of disinfection some cysts survived this procedure. Chlorhexidine exhibited a dose-response kill curve but the most effective concentrations are also corneo-toxic. Polyaminopropylbiguanide (0.00005%) has good effectiveness against the cyst but was not completely cidal at the dose tested. Thimerosal (0.002%) and hydrogen peroxide (3%) were found to be without effect. These findings should give contact lens practitioners guidelines for selecting a disinfection system for their patients.