We quantified the number of microparticles in plasma of six patients with chronic thromboembolic pulmonary hypertension (CTEPH) and age- and sex-matched pulmonary embolic (PE) and healthy controls and investigated the role of microparticle endoglin in the regulation of pulmonary endothelial function in vitro. The gene discussed is ENG; the disease is chronic thromboembolic pulmonary hypertension.