I have read with great interest the article published by Carratelli et al [C.R. Carratelli. I. Nuzzo, D. Cozzolino, C. Bentivoglio, R. Paolillo, A. Rizzo, Relationship between Chlamydia pneumoniae infection, inflammatory markers, and coronary heart diseases. Int Immunopharmacol. 6 (5) 2006 848-53]. Briefly they have reported increased levels of inflammatory markers and elevated titers of IgG and IgA of C. pneumoniae by using both ELISA and MIF method. There are several factors which may underly the controversial results of scroepidemiological studies. I have commented on the report of Carratelli et al. regarding the some of these factors. (c) 2006 Elsevier B.V. All rights reserved.