The role of tumor necrosis factor alpha (TNF-alpha) in Chlamydia pneumoniae atherogenesis was evaluated in TNF-alpha p55 receptor-deficient C57BL/6J mice fed a high-fat/high-cholesterol diet. No acceleration of atherosclerotic lesion development was observed in infected mice compared to uninfected mice, indicating that TNF-alpha plays a role in the acceleration of atherosclerosis by C. pneumoniae.