Nitric oxide (NO) reduces the severity of pulmonary vascular disease in rats as do elastase inhibitors. We therefore hypothesized that NO inhibits elastase by suppressing mitogen‐activated protein kinases that trans‐activate AML1B, a transcription factor for elastase. We used cultured pulmonary artery smooth muscle cells in which serum‐treated elastin (STE) induces a > threefold increase in elastase activity as evaluated by solubilization of [³H]‐elastin. NO donors (SNAP and DETA NONO‐ate) inhibited elastase in a dose‐dependent manner as did a cGMP mimetic (8‐pCPT‐cGMP). SNAP inhibition of elastase was reversed by coadministration of a cGMP‐PKG inhibitor (Rp‐8‐pCPT‐cGMP). The STE‐induced increase in phospho‐ERK was suppressed by NO donors and the cGMP mimetic, and reversed by cGMP‐PKG inhibitor, as was expression of AML1B and DNA binding in nuclear extracts. A concomitant increase in p38 phosphorylation was also inhibited by SNAP, but whereas MEK inhibitor (PD98059) suppressed elastase and AML1B‐DNA binding, a p38 inhibitor (SB202190) did not. Our study uniquely links NO with inhibition of elastase‐dependent matrix remodeling in vascular disease by suggesting a cGMP‐PKG‐related mechanism suppressing ERK‐mediated partitioning of AML1B in nuclear extracts.—Mitani, Y., Zaidi, S. H. E., Dufourcq, P., Thompson, K., Rabinovitch, M. Nitric oxide reduces vascular smooth muscle cell elastase activity through cGMP‐mediated suppression of ERK phosphorylation and AML1B nuclear partitioning. FASEB J. 14, 805–814 (2000)