Atherosclerosis is an insidious disease with serious morbidity and mortality including ischemic heart disease, stroke, and myocardial infarction. This condition is progressive and can start early in life eventually leading to large plaques and arterial occlusion. Two key components of this process are the immune system and lipids; in particular, LDL which accumulates within the arterial walls and macrophages which recognize and engulf oxidized-LDL (oxLDL) to form foam cells. Knowing that certain antibodies directed against bacterial antigens such as phosphorylcholine (PC) and cardiolipin (CL) show opsonizing cross-reactivity with oxLDL it can be proposed that there is a link between immune responses to periodontal bacteria and atherosclerosis. The aim of this investigation was to determine whether periodontal bacteria are capable of inducing serum antibodies potentially involved in cardiovascular diseases; specifically, IgG anti-PC, IgG anti-CL, and IgM anti-CL. To test this, 17 subjects with chronic periodontitis received scaling and root planing in conjunction with blood sample analysis to determine if periodontal instrumentation resulted in changes in these serum antibodies. If plaque bacteria are responsible for an immune response then serum levels of these antibodies should decrease following periodontal therapy. We found that serum levels of IgG anti-PC, IgG anti-CL, and IgM anti-CL decreased following periodontal scaling and root planing but the change was significant only for IgG anti-PC (P 0.045). Serum levels of IgM anti-CL approached significance (P 0.054). The results support the hypothesis that the immune response to periodontal bacterial microflora contributes to serum concentrations of antiphospholipid antibodies.