MPO and abdominal aortic aneurysm: •Key Findings: Montelukast treatment significantly reduced aortic diameter expansion (P < .01) and matrix metalloproteinase-2/matrix metalloproteinase-9 expression (P < .05), decreased myeloperoxidase activity (P < .01), and restored superoxide dismutase levels (P < .05) compared with untreated abdominal aortic aneurysm rats.