The aim of this study was to investigate the ultrastructural and immunohistochemical organization of the main collagenous components of healthy human keratinized mucosa surrounding endosseous implants. Eight patients with completely edentulous mandibles were selected. Four endosseous implants were placed in the mandible of each patient, connected with a bar to support a complete overdenture, and loaded 4 months later. Two years after placement, biopsies of surrounding soft tissue, including the sulcular and junctional epithelium with the underlying and supracrestal connective tissue, were routinely prepared for standard electron microscopy and for ultrastructural immunolabeling of Types I, III, and IV collagen. The connective tissue located under the junctional epithelium comprised Types I and III collagen, whereas the supracrestal connective tissue was composed mainly of Type I collagen. Type IV collagen was located exclusively in the basement membrane of the junctional epithelium. Keywords: collagen, immunotyping, peri-implant mucosa, ultrastructure