The efficacy of photodynamic therapy tumor destruction is dependent upon both the interruption of the tumor vasculature and the resultant production of unstable oxygen species causing cellular oxidation and death. Chloroaluminum sulfonated phthalocyanine (CASP) is a recently developed photosensitizer. In order to study the direct vascular effects of CASP on a non-tumor system, a rat window chamber was utilized. Twelve rats were implanted with the window chamber, and were divided into two groups of six. Three rats served as controls for each group (receiving light alone, CASP alone, or no treatment). The remaining 6 rats received 10 mg/kg CASP intravenously 4 days after chamber placement. Photoactivation with light was performed 24 hours after injection (power density 200 mW/cm2, irradiance 100 J/cm2, lambda = 675 nm). Utilizing integrating sphere measurements and image analysis, marked vascular changes in the form of initial vasospasm followed by vaso-constriction and loss of chamber neovascularization were noted in the CASP-PDT group. The control groups exhibited no significant changes. Manipulation of the chamber vasculature at strategic time-points may translate into improved response rates for photodynamic therapy in a tumor model.