Bosentan is an endothelin receptor antagonist used as a first-line treatment in pulmonary arterial hypertension (PAH). Its main adverse effect is a dose-dependent liver toxicity. CYP2C9*2 has recently been shown to be associated with hepatotoxicity in PAH patients. We conducted a nested case-control study to further explore the relationship between functional polymorphisms of gene products involved in bosentan pharmacokinetics (OATP1B1, OATP1B3, and CYP2C9) or hepatobiliary transporters affected by bosentan (ABCB11) and bosentan-induced liver toxicity.