Recent studies have suggested that the periodontal disease, chronic sub-clinical inflammation, is associated with atherosclerosis, although "cause or effect" relationship is still unclear. The aim of this study was to assess the association between the degree of periodontal infection and lipid profiles in diabetic subjects. Additionally, the association of such sub-clinical inflammation with HMG-CoA reductase gene expression was evaluated. One hundred and thirty-one non-obese relatively well-controlled Japanese type 2 diabetic patients were enrolled for the study. Although no significant association was observed between serum triglycerides, HLD-cholesterol and antibody titer to Porphyromonas gingivalis (Pg), the most predominant periodontal pathogen in adults, LDL-cholesterol was significantly associated with antibody titer to Pg. Concomitantly, the same works out to be true for total cholesterol. To understand the possible mechanisms underlying this association, we evaluated 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase gene expression in cultured HepG2 cells stimulated by either bacterial lipopolysaccharide (LPS) or inflammatory cytokines. Although Pg and E. coli LPS had no effect on HMG-CoA reductase gene expression, both tumor necrosis factor-alpha and interleukin-6 (IL-6), especially IL-6 at low concentration, markedly up-regulated HMG-CoA reductase gene expression. It can be concluded that Pg infection is associated with increased LDL-cholesterol in diabetic subjects, which may be accompanied by increased cholesterol synthesis by inflammatory cytokines.