TOOKAD (WST09) is a new, long-wavelength palladium bacteriopheophorbide photosensitizer that targets tissue vasculature. The cutaneous phototoxicity of TOOKAD was assessed in normal rat and pig animal models and in patients in a Phase-I trial of TOOKAD-mediated photodynamic therapy (PDT) for recurrent prostate cancer. Controlled skin exposures were administered using solar-simulated light at various times after drug administration. Two different spectral ranges were used. In the first, the UV portion of the spectrum was removed (UV⁻) because UV irradiation in nondrugged control animals produced an erythema response at incident energy densities (J/cm²) lower than those required to induce a PDT response. In the second, the full solar spectrum (UV ) was used, and the potentiation by the photosensitizer of the UV-mediated minimum erythema dose was assessed. Results showed that the PDT skin response was negligible at clinical drug doses of 2 mg/kg for any period after administration at light doses of 128 J/cm² in the animal models. In patients, there was no observed UV⁻ skin response at doses of up to 2 mg/kg, drug–light intervals of 1–3 h or greater and light exposures up to 128 J/cm². At higher drug doses in the rat and pig models, the duration of skin phototoxicity was found to be ∼3 h and less than 1 h, respectively. Using the full spectrum of solar-simulated light, the presence of TOOKAD did not measurably enhance the UV -induced erythema in the rats, pigs or patients.