BACKGROUND: Pulmonary arterial hypertension is a serious complication in scleroderma and early diagnosis is warranted. PATIENTS AND METHODS: 33 Scleroderma patients (mean age 54 [SD 11] years) with normal systolic pulmonary artery pressure (sPAP), right and left ventricular parameters at rest were enrolled in this study. They were investigated by echocardiography during physical exercise and hypoxia. A hypertensive pulmonary vascular reaction was diagnosed when sPAP inappropriately increased during exercise compared to individual exercise tolerance, or if sPAP was >40mm Hg during hypoxia exposure, respectively. RESULTS: In 17 patients there was a normal increase of sPAP at exercise of 34 [8]mm Hg (mean VO2 max 70 [17]% predicted), and 29 [5]mm Hg during hypoxia. Sixteen patients developed a hypertensive pulmonary vascular response with a sPAP of 47 [9]mm Hg during exercise (VO2max 64 [15]% pred.), and 54 [7]mm Hgmm Hg during hypoxia, respectively. The sPAP/VO2 max ratio was higher in patients with a hypertensive response (0.76 [0.17] vs. 0.49 [0.12] p<0.0001). There was no difference in scleroderma subtype, duration of disease, gender or age between groups. During a 3-year follow up one patient with a hypertensive response developed manifest pulmonary arterial hypertension. CONCLUSION: Non-invasive assessment of pulmonary circulation during physical exercise and/or hypoxia enables screening for pulmonary vascular dysfunction in scleroderma.