Pulsed dye laser (PDL) is the gold standard treatment for port-wine stains (PWS). However, the outcomes are highly variable due to the new angiogenesis occurring after laser irradiation. Studies suggest that endothelin is involved in the neoangiogenesis that occurred after treatment of port-wine stains by PDL. The main objective of this pilot clinical trial is to evaluate the effectiveness and safety of an inhibitor of endothelin orally taken, the Bosentan, following PDL treatment. Four patients with facial port-wine stain resistant to the PDL treatment will be included. The treatment by Bosentan (2 mg/kg twice daily, maximum 62,5 mg twice daily) will be given one day before the PDL irradiation and continued for 14 days. Only one test area of PWS will be treated with PDL. The primary outcome measure will be an important or complete improvement (Investigator Global Assessment 3 or 4) between treated area and non treated one, 14 days after the end of the treatment which corresponds to one month after the laser PDL session. The evaluation will been performed on standardized pictures by 2 independent physicians blinded to the region treated or not.