Pulmonary arterial hypertension (PAH) is a severe disease usually diagnosed by echocardiography and further confirmed by right heart catheterisation. Follow-up under treatment consists in assessment of clinical signs, various types of exercise testing and repeated echocardiograms. Several molecules which can be measured in the blood or sometimes in other biological fluids are known to be elevated in PAH. The most extensively studied are members of the family of natriuretic peptides, uric acid, and products generated by nitric oxide activity. Due to the low prevalence of PAH and their suboptimal specificity, these potential markers are generally of modest positive predictive value which precludes their use as screening tools. However, some of them correlate significantly with prognosis, and thus, in conjunction with classical clinical and paraclinical parameters, they may be a further aid to clinical decision-making for the specialist dealing with PAH patients.