Adult periodontitis, which is the major cause of adult tooth loss, is commonly characterized by chronic inflammatory disease caused by infection with periodontopathic bacteria such as Porphyromonas gingivalis. Our aims in the present study were to examine the expression of endothelin-1 (ET-1) in cultured HEp-2 epithelial cells after infection with P. gingivalis, and in gingival tissue from adult periodontitis patients. The cell lines were infected with the strains P. gingivalis 33277 and 381 for assessment of bacterial invasion using an antibiotic protection assay, and the expression of ET-1, inflammatory cytokines and cell adhesion molecules was examined by ELISA and reverse transcription-PCR. The expression of ET-1, as well as that of interleukin-1 beta, interleukin-8 and ICAM-1 (intercellular cell adhesion molecule 1), was induced significantly in a time-dependent manner, whereas the expression of MCP-1 (monocyte chemotactic protein-1), RANTES (regulated upon activation, normal T-cell expressed and secreted) and VCAM-1 (vascular cell adhesion molecule 1) was not. Furthermore, in gingival tissues from adult periodontitis patients, we also observed increased expression of ET-1 mRNA compared with tissue from normal healthy donors. These results suggest that infection by periodontopathic bacteria up-regulates the expression of ET-1, together with that of inflammatory cytokines and ICAM-1, in gingival epithelial cells, and that ET-1 expression may be closely involved in the regulation of cytokine responses and cell-cell adhesion in adult periodontitis lesions.