The aim of the present investigation was to study some tissue characteristics of the ridge mucosa before and after implant installation. 9 partially edentulous patients were included in the study. At the time of fixture installation, 1 recipient site in each patient was selected for soft tissue biopsy. Abutment connection and restorative therapy were performed after 3-6 months. When the implants had been in function for about 6 months, a soft tissue sample was obtained from the keratinized peri-implant mucosa at the 1 implant site from which the first biopsy was obtained. Each biopsy was divided into 1 mesial and 1 distal portion. The mesial tissue portion was fixed in a buffered fixative and embedded in EPON. Sections were produced, stained in PAS and toluidine blue and used for histometric and morphometric analyses. The distal portion of the biopsies were embedded, snap frozen in liquid nitrogen and stored in a freezer at -70 degrees C. From each tissue portion, 15 sections were prepared in a cryostat and exposed to immunohistochemical staining. A panel of monoclonal antibodies was used and the avidin-biotin method for staining was applied. The sections were examined morphometrically. Both tissues harbored a well keratinized oral epithelium and a connective tissue, the composition of which was close to identical in terms of collagen, cells and vascular structures. The peri-implant mucosa, however, also included a junctional epithelium which evidently allowed the penetration of products from the oral cavity. As a consequence, the periimplant mucosa in comparison to the masticatory mucosa was found to contain significantly enhanced numbers of different inflammatory cells.