The study by van der Ven et al1 showed antibodies to Chlamydia pneumoniae to be significantly associated with atherosclerosis and renovascular disease in patients with hypertension and a strongly suspected renal artery stenosis. The specific IgG or IgA antibodies used in the study, however, do not necessarily distinguish between persistence of real infections and only a previous contact. Specific IgG-containing immune complexes for C pneumoniae have been demonstrated to be more sensitive markers of a real infection.2