In vitro and animal studies revealed micro-RNAs (miRs) to be involved in modulation of hypoxia-induced pulmonary hypertension (HPH). However, knowledge of circulating miRs in humans in the context of HPH is very limited. Since symptoms of HPH are nonspecific and noninvasive diagnostic parameters do not exist, a disease-specific and hypoxemia-independent biomarker indicating HPH would be of clinical value. To examine whether plasma miR levels correlate with hypoxia-induced increase in pulmonary artery pressures, plasma miRs were assessed in a model of hypoxia-related pulmonary hypertension in humans exposed to extreme altitude. Forty healthy volunteers were repetitively examined during a high-altitude expedition up to an altitude of 7,050 m. Plasma levels of miR-17, -21, and -190 were measured by real-time quantitative PCR and correlated with systolic pulmonary artery pressure (SPAP), which was assessed by echocardiography. A significant altitude-dependent increase in circulating miR expression was found (all P values < 0.0001). Compared with baseline at 500 m, miR-17 changed by 4.72 ± 0.57-fold, miR-21 changed by 1.91 ± 0.33-fold, and miR-190 changed by 3.61 ± 0.54-fold at 7,050 m (means ± SD). Even after adjusting for hypoxemia, miR-17 and miR-190 were found to be independently correlated with increased SPAP. Progressive hypobaric hypoxia significantly affects levels of circulating miR-17, -21, and -190. Independently from the extent of hypoxemia, miR-17 and -190 significantly correlate with increased SPAP. These novel findings provide evidence for an epigenetic modulation of hypoxia-induced increase in pulmonary artery pressures by miR-17 and -190 and suggest the potential value of these miRs as biomarkers for HPH.