Syndecans are transmembrane heparan sulfate proteoglycans. They are known to interact with basic fibroblast growth factor (bFGF), and it has been suggested that they play important roles in the growth, morphology, and migration of a variety of cell types. We examined the expression of syndecans and fibroblast growth factor receptor type 1 (FGFR1) in periodontal ligament (PDL) cells, because these membrane proteins may play roles in the control of growth and differentiation during regeneration of PDL. Reverse-transcription/polymerase chain-reaction (RT-PCR) showed that PDL cells expressed syndecan-2 and -4 mRNAs. This was confirmed by sequence analysis of the PCR products. When PDL cells were maintained for 25 days, alkaline phosphatase (ALPase) activity gradually increased and reached a maximal level on day 20. Northern blotting analysis showed that PDL cells expressed 2.3-kb syndecan-2, 2.6-kb syndecan-4, and 2.8-kb FGFR1 mRNAs throughout the entire culture period, whereas no syndecan-1 mRNA was detectable by this method. Maximal levels of syndecan-2, -4, and FGFR1 mRNAs were observed on day 5. However, their levels were markedly decreased on days 20 and 25. Accordingly, the inhibitory effect of bFGF on ALPase activity was less on day 20 than on day 5. When PDL cells were pre-treated with heparitinase, a mitogenic response of PDL cells to bFGF was decreased. These observations indicate that PDL cells express syndecan-2, -4, and FGFR1 mRNAs, and that those levels are changed with the increase in ALPase activity in culture. The reductions in syndecan-2, -4, and FGFR1 levels may be involved in the control of growth and differentiation of PDL cells during development and regeneration.