Psoralen activated by UVA light (PUVA) was investigated as a means of inhibiting smooth muscle cell proliferation resulting from balloon injury. Twenty kilogram domestic swine were anesthetized and underwent balloon angioplasty to create a 133% overstretch injury. Assignments of treatment and control were randomized between the left anterior descending (LAD) and circumflex (LCX) coronaries arteries. The animals were given with 5 mg/kg of 8- methoxypsoralen eternally. Treatment vessels received 600 mJ/cm 2 of 364 nm light during balloon inflation to activate the psoralen. Control vessels received drug and balloon injury only. Serum was obtained during the light delivery to assess psoralen levels. At 30 days, animals were sacrificed and the coronary arteries perfusion fixed. Five sections per vessel were analyzed morphometrically to determine percent intimal area and extent of injury. The restenosis injury index was 0.21 plus or minus .02 in treatment vessels and 0.14 plus or minus .01 in the controls with a p-value less than .02. In this large animal model of balloon angioplasty injury, psoralen activated by ultraviolet light increased intimal hyperplasia.