CD44s (standard form) is an integral membrane glycoprotein, which plays an important role in both cell-cell and cell-substrate adhesion. Few studies have demonstrated that CD44s and its isoforms are involved in mediating cell-cell and cell-substrate interactions in the periodontium and surrounding tissues. The present study was undertaken as so little data are available on its presence in human adult hard dental structures. Six extracted premolars from children, aged 10-12 years, were used in the present study. They were fixed in 10% neutral buffered formalin and decalcified in 7.5% EDTA for 2 weeks. Immunohistochemistry to reveal binding of a monoclonal mouse anti-CD44s was used for the localization of CD44s. The antibody was applied directly onto the tissue section and the slides incubated overnight (4 degrees C) in a humidified chamber. In serial sagittal sections of teeth, binding of anti-CD44s was seen in odontoblasts, periodontal ligament fibroblasts and cementoblasts. Our findings present evidence that CD44s is localized in periodontal ligament fibroblasts, cementocytes and odontoblasts of mature human teeth. CD44s may be involved in tooth cell differentiation and later in cell-matrix interaction and in the accumulation of inflammatory cells in the extravascular connective tissue in these sites.