High-grade squamous intraepithelial lesion (H-SIL) is an extremely frequent precancerous cervical lesion, leading to invasive cervical cancer if undetected and untreated. We are currently evaluating two new noninvasive methods for detection and treatment of H-SIL photodynamic therapy (PDT) and frequency domain photon migration (FDPM). PDT induces selective necrosis of dye sensitize malignant tissues when activated with light of appropriate wavelength. FDPM is a near-infrared spectroscopy technique for determining optical properties (i.e. absorption and scattering of light, ua and uUs) of tissues. Our objectives are 1) To determine the feasibility, safety, and efficacy of using PDT to treat H-SIL, 2) To quantitatively determine ua and uUs of normal cervical tissue and H-SIL in vivo, and to calculate physiologic parameters, specifically absolute concentration of oxy/deoxyhemoglobin and water in cervical tissue, 3) To assess the feasibility of differentiating normal cervical tissues from H-SIL based on the optical properties, 4) to monitor how cervical tissue optical and physiological properties change in response to PDT, 5) To optimize PDT light dosimetery and clinical outcome based on optical property measurements.