In the present study, the analysis of MMPs levels in plasma and tissues in patients with aneurysmal lesions identified several patterns of protease activity. Levels of both MMP-9 and NGAL were increased in aneurismal vessels, while the patterns of MMP-9 and NGAL expression was very high in all patients with ruptured aneurysm, both central and peripheral. These results show: 1) the chronic and degenerative nature of the aneurysmal lesion which is associated with increased levels of inflammatory proteinases, like MMP-9; 2) the apparent pivotal role of MMP-9 and NGAL in the pathophysiologic processes which lead to the final stage of natural history of aneurysms; and 3) the ubiquitous distribution of MMP-9 and NGAL. The pattern increased expression of MMP-9 and NGAL appears to be specific for aneurysmal arteries and it is not dependent on the anatomic site of the lesion.