Disclosed are crystalline forms of bosentan (4-tert-butyl-N-[6-(2-hydroxyethoxy)-5-(2-methoxyphenoxy)-2-(2-pyrimidinyl)-pyrimidin-4-yI]-benzenesulfonamide), characterized by an X-ray diffraction pattern comprising peaks at 4.02, 6.12, 8.38, 9.39,10.04,15.26,17.72, 17.98, 18.81, 19.28,20.31,21.05,27.57,31.91 and 45.65 plus or minus 0.2 degrees theta. The crystalline form of bosentan is useful for treating or preventing an endothelien receptor mediated disorder such as cardiovascular disorders. Specific cardiovascular disorders treated include hypertension, pulmonary hypertension, ischemia, vasospasm or angina pectoris.
