In photodynamic therapy, systemic administration of photosensitizing agents induces cutaneous photosensitization in patients. This side-effect can be avoided by topical administration of the agents when only surface lesions are involved. A hydroalcoholic solution of tetrasodium-meso-tetraphenylporphinesulfonate (TPPS) containing Azone, a percutaneous penetration enhancer, was investigated to evaluate its photosensitizing potential in the treatment of 33 primary and recurrent neoplastic lesions of the skin. A complete remission was obtained of lesions with clinical thickness of less than 2 nun. Treatment effectiveness depends on both light and drug penetration through skin. Further studies are in progress to optimize treatment parameters.