 Sildenafil is a cyclic GMP selective phosphodiesterase type 5 inhibitor approved for use by the FDA in patients with pulmonary arterial hypertension. There has been recent interest in the use of the drug in patients with diffuse parenchymal lung diseases. This is largely based on sildenafils salutary effects observed in small studies Collard et al. 897-99;Ghofrani et al. 895-900;Collard et al. 897-99 and the frequent coexistence of pulmonary hypertension in these patients Nathan et al. 657-63. In eight patients with pulmonary fibrosis and pulmonary hypertension, sildenafil reduced pulmonary artery pressure and improved shunt fraction as determined by multiple inert gas elimination technique Ghofrani et al. 895-900;Nathan et al. 657-63. Collard et al demonstrated a 49 meter improvement in 6 minute walk distance in 11 patients with idiopathic pulmonary fibrosis and pulmonary hypertension after 3 months of therapy with sildenafil. 