In a rabbit model, endometriotic lesions were utilized to study hematoporphyrin derivative (HPD) uptake and the effect of photoradiation using the gold vapor laser. Morphological studies confirmed successful induction of ectopic endometrial growth and the lesions displayed preferential HPD uptake compared to normal intraperitoneal structures. Gold vapor laser irradiation of the lesions in HPD pretreated animals produced necrosis of the endometriotic lesions leaving surrounding tissues healthy. Results from this study suggest that HPD-mediated photodynamic therapy may be a suitable means of treating endometriosis in the human.