OBJECTIVE To evaluate immunohistochemical staining of the endothelia of corneas from patients with clinical diagnoses of iridocorneal endothelial (ICE) syndrome. METHODS Corneas diagnosed with ICE syndrome and removed during corneal transplantation were freshly frozen, sectioned, and stained with monoclonal antibodies to keratin subgroups, vimentin, desmin, and a series of other antibodies against intermediate filaments. Transmission electron microscopy was performed on segments of these corneas fixed in glutaraldehyde. RESULTS There was almost universal staining of the endothelial layer with A1 and A3 keratin monoclonal antibodies and vimentin. Transmission electron microscopy of the corneas also confirmed features consistent with keratin. CONCLUSIONS The "endothelial" cell layer in the iridocorneal endothelial syndrome has electron microscopic and immunohistochemical characteristics of epithelial-like cells, but it also cross-reacts with vimentin, suggesting that these cells retain or derive some endothelial staining characteristics as well. This "epithelialization" of the endothelial layer may explain the progressive cellular proliferation across angle and iris similar to that seen in iatrogenic epithelial downgrowth and posterior polymorphous endothelial dystrophy.