Primary pulmonary hypertension (PPH) represents the end stage of a disruption of pulmonary vascular integrity, of unknown cause. Although PPH is associated with several systemic disorders, there have hitherto been few clues as to the aetiological factors responsible for the pathogenesis of this condition. As an example of the application of modern molecular genetics and positional cloning, this leader describes the range of studies currently under way, which aim to find the gene that underlies PPH, and summarises the implications of the identification of such a gene.