['Results of many studies show that apolipoprotein B (apo B) is a better marker of risk of vascular disease than other lipid markers including LDL and HDL-cholesterol and triglycerides. We investigated the association between two infectious agents: C. pneumoniae and H. pylori, known to have an atherogenic effect, and apo B, to evaluate the effects of chronic infections on apo B levels.', 'The study group consisted of 257 patients in whom diagnostic coronary angiography was performed. C. pneumoniae IgG and IgM and H. pylori IgG and IgA antibodies were measured by enzyme-linked immunosorbent assay and apo B levels were measured by the nephelometry method. Established risk factors of atherosclerosis were recorded. Of 257 patients recruited, 104 had normal vessels, 88 had 3 or more vessels obstructed and 65 had ectatic vessels without atherosclerosis. Mean apo B concentration was significantly higher in C. pneumoniae IgG and IgM positive healthy subjects compared with C. pneumoniae negatives (0.954 vs. 0.722 and 0.973 vs. 0.851, p < 0.001 and p = 0.007, respectively). Apo B levels were significantly higher in severe atherosclerotic patients (0.985 +/- 0.234 g/l) compared with control subjects (0.892 +/- 0.244 g/l) (p = 0.008), but the difference was not significant in ectatic subjects (0.946 +/- 0.272 g/l) when compared with controls (p = 0.18). Apo B levels were higher but not statistically significant in H. pylori antibody positive cases when compared with negatives.'] Is infection with Chlamydia pneumoniae but not Helicobacter pylori related to elevated apolipoprotein B levels?