Despite recent advances in medical treatment, pulmonary arterial hypertension (PAH) continues to be associated with high morbidity and mortality. While the diagnosis is established via a right heart catheterisation, current non-invasive measures of disease severity and response to treatment used in clinical practice are the 6-min walk distance and the World Health Organization functional class. Although both parameters correlate with disease severity and prognosis, they have significant limitations. A major shortcoming in assessing PAH is lack of standardised, non-invasive, objective parameters that function as biomarkers to help assess the severity and prognosis of disease and to follow patients' response to treatment. In this article, we will review current knowledge on potential biomarkers associated with diagnosis, prognosis and response to treatment of PAH. Most biomarkers are either being evaluated for potential use in clinical practice, or being used as research tools.