We evaluate Photofrin-mediated photodynamic therapy (PDT) in a phase 2 clinical trial as an adjuvant to surgery to treat peritoneal carcinomatosis. We extract tissue optical [reduced scattering (µ's), absorption (µa), and attenuation coefficients (µeff)] and physiological [blood oxygen saturation (%StO2), total hemoglobin concentration (THC), and photosensitizer concentration (cPhotofrin)] properties in 12 patients using a diffuse reflectance instrument and algorithms based on the diffusion equation. Before PDT, in normal intraperitoneal tissues %StO2 and THC ranged between 32 to 100% and 19 to 263 µM, respectively; corresponding data from tumor tissues ranged between 11 to 44% and 61 to 224 µM. Tumor %StO2 is significantly lower than oxygenation of normal intraperitoneal tissues in the same patients. The mean (±standard error of mean) penetration depth (δ) in millimeters at 630 nm is 4.8(±0.6) for small bowel, 5.2 (±0.67) for large bowel, 3.39(±0.29) for peritoneum, 5.19(±1.4) for skin, 1.0(±0.1) for liver, and 3.02(±0.66) for tumor. cPhotofrin in micromolars is 4.9(±2.3) for small bowel, 4.8(±2.3) for large bowel, 3.0 (±1.0) for peritoneum, 2.5(±0.9) for skin, and 7.4(±2.8) for tumor. In all tissues examined, mean cPhotofrin tends to decrease after PDT, perhaps due to photobleaching. These results provide benchmark in-vivo tissue optical property data, and demonstrate the feasibility of in-situ measurements during clinical PDT treatments.