Diagnosis and management of Acanthamoeba chronic ulcerative keratitis is difficult. Two cases of Acanthamoeba keratitis at Wills Eye Hospital were diagnosed within several months of each other during 1983. Corneal transplantation was necessary for diagnosis and therapy in these cases. Another two cases were diagnosed when histopathologic specimens from penetrating keratoplasties done between 1974 and 1983 were reviewed retrospectively. There has been no evidence of recurrent disease in any of our cases during follow-up periods averaging two years (range, 12 to 40 months). The diagnosis of Acanthamoeba keratitis must be considered in cases of chronic progressive corneal ulceration unresponsive to medical therapy.