We thank Montani and colleagues for their response to our article,1 which suggested that pulmonary venoocclusive disease (PVOD) should be considered as an alternative diagnosis in patients with pulmonary arterial hypertension who do not respond to medical therapy. We recognize that the reported rate of PVOD in this study is higher than that previously documented in literature on pulmonary hypertension. This may be attributable to two factors. First, the study was performed in a selected group of patients with pulmonary hypertension who had not responded to medical therapy and for whom, consequently, an alternative diagnosis was more likely. Second, a novel stain using routine smooth muscle actin immunohistochemistry with a Verhoeff elastin counterstain allowed concurrent examination of the vessel elastic lamina and smooth muscle hypertrophy in any one vessel. In conjunction with vessel microanatomical location, this enabled accurate differentiation between arterial and venous vessels, and allowed qualitative assessment of the occlusion as smooth muscle cells or fibrous tissue proliferation within the vessel wall. Smooth muscle actin immunohistochemistry with Verhoeff elastin counterstaining may have enabled higher and more accurate detection of PVOD.