Structural observations upon fluorosed enamel were made on human teeth extracted from Nabeul (Tunisia). Longitudinal sections of enamel were made and microradiographed. Topographical observatoons in the S.E.M. showed alterations of the pattern of mineralization. Fissures and clefts filled with plaque material were observed to reach to the surface of the teeth. They penetrated into enamel along the prisms. Acid etching of the surface by 30% H3PO4 revealed enlarged acid-resistant sheaths while the core of the prisms was irregularly etched. Inner portions of the enamel were observed on fractured fragments. The structure was not significantly perturbated except for areas of porosity. After demineralization of the sections by 10% EDTA at pH 7 and critical point drying, the organic matrix was observed in the S.E.M. : It appeared as a fibrous network. Compared with sound teeth the matrix was dense and irregular. Histochemical stainings showed the presence of organic material. Alcian blue and PAS positive contents were very low except near the enamel-dentine junction. Preliminary observations were made using SMI Cameca ion microanalyser and histochemical studies on undecalcified sections were made in order to compare the observations made with light microscopy with S.E.M. findings.