Background and Objectives: Early growth response-1 is a nuclear transcription factor implicated in regulating cell proliferation. Fibroblast growth factor-1 is the prototypic fibroblast growth factor involved in the proliferation and differentiation of various cell types. Expression of early growth response-1 induced by fibroblast growth factor-1 thus may be very important for cell growth, during both development and wound healing in oral tissue. However, little is known about the expression and kinetics of early growth response-1 in fibroblast growth factor-1-stimulated oral cells. The aim of this study was to investigate the effects of fibroblast growth factor-1 on the expression of early growth response-1 in human periodontal ligament cells. Material and Methods: Periodontal ligament cells were cultured in medium containing 1, 10 or 100 ng/mL of fibroblast growth factor-1 for 45 min or with 10 ng/mL of fibroblast growth factor-1 for 15, 30, 45, 60 or 120 min. The proliferation of periodontal ligament cells was evaluated by measuring 5-bromo-2'-deoxyuridine incorporation. The expression of early growth response-1 mRNA and protein, and the localization of early growth response-1 protein, were examined by western blotting, northern blotting and immunocytostaining. Results: 5-Bromo-2'-deoxyuridine incorporation correlated directly with increases in fibroblast growth factor-1 concentration, and 5-bromo-2'-deoxyuridine incorporation peaked 45 min after starting treatment. Early growth response-1 protein was expressed in response to a concentration of fibroblast growth factor-1 as low as 1 ng. Peak expression of early growth response-1 mRNA was observed at 15 min and that of early growth response-1 protein at 60 min. The 140-kDa early growth response-1 protein was not detected in the nuclear fraction, and the peak expression of the 80-kDa early growth response-1 protein occurred at 60 min. Early growth response-1 localized in or around the nucleus at 30 min. Conclusion: These results show that a concentration of fibroblast growth factor-1 as low as 1 ng induces the expression of early growth response-1 protein, and that the 80-kDa early growth response-1 protein functions in the nucleus of periodontal ligament cells treated with fibroblast growth factor-1.