Two fibroblast populations derived from free and attached gingiva (FGF, AGF) have been compared in cell culture. They exhibited the same morphology and similar cytoskeletal staining patterns, but were different in glycosaminoglycan (GAG) synthesis. FGF released larger quantities of GAGs than AGF in the medium. The extracellular accumulation of hyaluronic acid was higher in FGF than in AGF, whilst the reverse pattern was observed intracellularly. In the case of sulphated GAGs the extracellular concentration, compared to HA, was higher in AGF, while the intracellular concentration was higher in FGF. The two cell populations responded differently to phenytoin (PHT) administration. PHT treatment increased the proportion of intracellular sulphated GAGs in AGF and of extracellular sulphated GAGs in FGF.