Thirteen skin biopsies were performed on 8 patients at different stages of skin sclerosis in chronic graft-versus-host disease (GVHD). On the same skin biopsies an immunostaining with antibodies directed against Types I and III procollagen, Types I, III, IV, V collagen, and laminin, and an ultrastructural study were performed. Alterations were observed at the dermal-epidermal junction and in the superficial dermis with a large deposit on Type III procollagen in the incipient scleroses and of Type I procollagen in the oldest ones. In this sclerotic superficial dermis, collagen fibers of irregular diameter were associated with mast cells and active fibroblasts, macrophages, and lymphocytes in close contact. The skin sclerosis in chronic GVHD might be considered a form of cutaneous fibrosis with features of excessive tissue repair related to an immunologic reaction between lymphocytes of the graft and tissue host cells.