Background: Abdominal aortic aneurysms (AAAs) are associated with chronic inflammation, disruption of medial elastin, and increased local production of elastolytic matrix metalloproteinases (MMPs). The purpose of this study was to investigate how treatment with a hydroxamate-based MMP antagonist (RS 132908) might affect the development of experimental AAAs. Methods: Male Wistar rats underwent intraluminal perfusion of the abdominal aorta with 50 units of porcine pancreatic elastase followed by treatment for 14 days with RS 132908 (100 mg/kg/day subcutaneously; n = 8) or with vehicle alone (n = 6). The external aortic diameter (AD) was measured in millimeters before elastase perfusion and at death, with AAA defined as an increase in AD (ΔAD) of at least 100%. Aortic wall elastin and collagen concentrations were measured with assays for desmosine and hydroxyproline, and fixed aortic tissues were examined by light microscopy. Results: AAAs developed in all vehicle-treated rats, with a mean AD (± SE) that increased from 1.60 ± 0.03 mm before perfusion to 5.98 ± 1.02 mm on day 14 (ΔAD = 276.4 ± 67.7%). AAAs developed in only five of eight animals (62.5%) after MMP inhibition, with a mean AD that increased from 1.56 ± 0.05 mm to 3.59 ± 0.34 mm (ΔAD = 128.1 ± 18.7%; P < .05, vs vehicle). The overall inhibition of aortic dilatation attributable to RS 132908 was 53.6 ± 6.8%. Aortic wall desmosine fell by 85.4% in the vehicle-treated rats (1210.6 ± 87.8 pmol/sample to 176.7 ± 33.4 pmol/sample; P < .05) but only by 65.6% in the animals treated with RS 312908 (416.2 ± 120.5 pmol/sample). In contrast, hydroxyproline was not significantly affected by either elastase perfusion or drug treatment. Microscopic examination revealed the preservation of pericellular elastin and a greater degree of fibrocollagenous wall thickening after MMP inhibition, with no detectable difference in the extent of inflammation. Conclusions: Systemic MMP inhibition suppresses aneurysmal dilatation in the elastaseinduced rodent model of AAA. Consistent with its direct inhibitory effect on various MMPs, RS 132908 promotes the preservation of aortic elastin and appears to enhance a profibrotic response within the aortic wall. Hydroxamate-based MMP antagonists may therefore be useful in the development of pharmacologic approaches to the suppression of AAAs.