OBJECTIVE: The objective of this study was to determine the photodynamic therapeutic response of U-87 human glioma cell in vitro as well as in the nude rat xenograft model using photofrin as photosensitizer. MATERIAL AND METHOD: U-87 cells were cultured on 96-well culture plates, photofrin(Quadralogic Technologies Inc., Vancouver, Canada) was added into the cell culture medium at concentration of 1ng/ml, 2.5ng/ml, 5ng/ml, 10ng/ml and 20ng/ml. 24 hour after drug treatment, cells were treated with optical(632nm) irradiation of 100mJ/cm2, 200mJ/cm2 and 400mJ/cm2. Photofrin(12.5mg/kg, i.p.) was administered to 28 nude rats containing intracerebral U-87 human glioma as well as 26 normal nude rats. 48 hours after administration, animals were treated with optical irradiation(632nm) of 35J/cm2, 140J/cm2 and 280J/cm2 to exposed tumor and normal brain. The photofrin concen-tration was measured in tumor and normal brain in a separate population of animals. RESULTS: By MTT assay, there was 100% cytotoxicity at any dose of photofrin with optical irradiation of 200mJ/cm2 and 400mJ/cm2. But at the optical irradiation of 100mJ/cm2 cells were killed in dose dependent manner 28.5%, 49.1%, 54.4%, 78.2%, and 84.6% at concentration of 1ng/ml, 2.5ng/ml, 5ng/ml, 10ng/ml and 20ng/ml, respectively. Dose dependent PDT lesions in both tumor and normal brain were observed. In the tumor lesion, only superficial tissue damage was found with optical irradiation of 35J/cm2. However, in the optical irradiation group of 140J/cm2 and 280J/cm2 the volume of lesions was measured of 7.2mm3 and 14.0mm3 for treatment at 140J/cm2 and 280J/cm2, respectively. The U-87 bearing rats showed a photofrin concentration in tumor tissue of 6.53+/-2.16ng/g, 23 times higher than that found in the contralateral hemisphere of 0.28+/-0.15ng/g. CONCLUSION: Our data indicate that the U-87 human glioma in vitro and in the xenografted rats is responsive to PDT. At these doses, a reproducible injury can be delivered to human glioma in this model. Strategies to spare the normal brain collateral damage are being studied.