Destructive remodeling of extracellular matrix has been shown to be present in aneurysmal abdominal aorta. We used real-time quantitative reverse transcriptase polymerase chain reaction to determine the relative expression of matrix metalloproteinase-13 (MMP13) in aortic tissue samples from patients who underwent abdominal aortic aneurysm repair operations (n = 36) and from nonaneurysmal autopsy samples (n = 20). The assays were carried out simultaneously in the same reaction tubes for ribosomal 18S RNA to correct for different amounts of input RNA. MMP13 was expressed in all parts of aorta and its expression was elevated in aneurysmal sac. In further studies using MMP13-specific antibody we demonstrated that MMP13 protein was present in the aneurysmal wall.