The aim of this study was to compare the response of cultured human gingival fibroblasts to two kinds of glass-ionomer cement in vitro with regards to understanding the biocompatibility of these materials and their suitability for use as subgingival restorative materials. The glass-ionomer cements tested were Ketac Fil, and GC Fuji II. These cements were mixed according to the manufacturers' directions and condensed into tissue culture wells or cavities prepared on the root surfaces of extracted teeth. Healthy root slices and untreated tissue culture wells were used as controls. Several features such as attachment, proliferation and morphology of cells were studied. The results indicated that cells could not attach to the glass-ionomer cements unless they had been washed with distilled water and tissue culture media. No significant difference in initial attachment (1.5h) and long term attachment (48h) between the groups tested was noted. No significant difference was observed between levels of proliferation for human gingival fibroblasts grown on Ketac Fil, Fuji II, root slices and culture wells. No significant alterations of the cytomorphology could be detected in glass-ionomer cement compared with root slices. These results indicate that provided the surface is adequately washed, Ketac Fil, and Fuji II may be acceptable subgingival root surface restorative materials.