The primary aim of the present study was to investigate the secretion of IL-1β and IL-18 from PBMCs of periodontitis patients and healthy controls after exposure of the cells to H2S. A second aim was to measure the capacity of subgingival bacteria to degrade cysteine and produce H2S, and to test the association between this H2S production and inflammation in the gingiva. The gene discussed is IL18; the disease is periodontitis.