It is known that prognosis of pulmonary hypertension (PH), especially connective tissue disease related PH (CTD-PH), is serious. CTD-PH is caused by not only pulmonary arterial hypertension, but also interstitial pneumonitis, hypoxia, chronic thromboembolism of pulmonary artery, or left heart diseases. Recently, prognosis of PH is improved by progress of diagnostic measures including echocardiography and development of effective vasodilators. However, early diagnosis of PH is necessary for further improvement of the prognosis. Previous reports have shown that diffusion lung capacity for carbon monoxide (DLco) is reduced in the early phase of PH, and we have shown that serum lactate dehydrogenase level is also elevated in this phase. Furthermore, we have been studying significance of stress echocardiography. Therefore, if reduced DLco or LDH elevation are recognized, follow up of laboratory data such as blood levels of KL-6, NT-proBNP, D-dimer, echocardiography, high resolution CT of the lung, in addition to clinical findings are important for prediction of PH.