In this study we have demonstrated that LPS from Porphyromonas gingivalis (LPS-PG) as well as hypoxia induces a NOX4-dependent increase in H2O2 release in PDL fibroblasts which may contribute to the development and progression of periodontal diseases when not balanced by a concomitant increase in antioxidative systems. The gene discussed is NOX4; the disease is periodontal disorder.