Trophozoite and cyst adherence of two Acanthamoeba keratitis strains (PHL/530 and PHL/978) to four types of unworn soft contact lens and their removal by cleaning agents were studied. Greater adherence of the trophozoites compared with the cysts was recorded for both strains. Trophozoites of PHL/530 adhered in greater numbers to type I lenses (61.4% poly[2-hydroxyethyl methacrylate-38.6% water), with no differences between type II (30% lidofilcon A-70% water), III (55% bufilcon A-45% water) and IV lenses (42% etafilcon A-58% water). Adherence of PHL/978 trophozoites to type II lenses was decreased compared with their adherence to the other lenses. Cysts of both strains showed greater adherence to type I and III lenses. Interstrain differences in trophozoite adherence occurred, with PHL/530 showing greater adherence to type I and II lenses. Recommended cleaning procedures using three commercial solutions were effective in removing Acanthamoeba from the lenses. This study indicates the possible role of adherence to contact lenses in the acquisition of Acanthamoeba keratitis, but shows that correct use of commercial cleaning agents may be important in the prevention of infection.