Recent increase in the incidence of whooping cough in several countries, has led the attention to the study of vaccine components and the expression of virulence factors in B. pertussis (Bp) under different physiological conditions. Bacterial pathogens face iron limitation during infection due to the presence of iron sequestering proteins in mammals.  In order to gain a wider view of the effect of iron concentration in protein expression, a proteomic strategy was adopted.  Whole cell extracts of Bp grown in the presence of the ion and during iron starvation were monitored through two-dimensional gel electrophoresis (2D-PAGE), and image analysis.  The resulting average protein maps contained a medium of 900 spots for each condition.  Statistical analysis of spot volumes in paired spots revealed the presence of 31 polypeptides displaying differential expression; 16 with lower expression in the presence of the ion and 15 with increased expression during iron starvation.  These spots and some major proteins with similar expression in both conditions were submitted to tryptic digestion and MALDI-TOF-MS.  Four landmark proteins were identified: they correspond to two chaperones, an enolase and a porin protein precursor.  Among proteins exhibiting higher expression in the absence of the ion, there were identified a superoxide dismutase (SodA), a hemin transport protein (BhuS), a hypothetical protein and a putative lipoprotein.  In addition, an acetyl transferase, displaying higher expression in iron-supplemented cultures, was detected. The increased expression of SodA has been correlated with the resistance of bacteria to the intracellular oxidative burst.  Also, a higher expression of hemin transport proteins might allow the capture of iron to supply the basic metabolic needs of the microorganism.  Identification of other differentially expressed proteins and the immune response elicited by these components in the host is actually under study.