This review presents the current clinical status of photodynamic therapy (PDT)in the treatment of human cancer, as well as its potential and the technical needs currently perceived as required for PDT to achieve that potential. Progress in the treatment of endobronchial cancer, superficial bladder cancer, head and neck cancer, gynecological cancer, intracranial tumors, gastrointestinal cancers, ocular cancers, and cutaneous and subcutaneous cancers is rev'ewed. While a nearly universal need is apparent for reliable, user-friendly PDT lasers, other technicAl advances in the mechanism of light delivery will be required to optimize treatment of intrdcranial, head and neck, gynecologic and intraocular tumors. Development of topical formulations of PHOTOFRINÃ‚Â® may allow treatment of gynecologic and cutaneous cancer while obviating the systemic photosensitivity caused by intravenous administration of the drug. Development of new photosensitizers activated at wavelengths above 630 nm may allow effective debulking or obliteration of large tumors. Indeed, in the future, specific photosensitizers may be tailored to different indications. Practical clinical situations should be considered when designing and testing new photosensitizers for future clinical development. Potential applications of POT in the intraoperative adjuvant therapy of tumors with a high risk of recurrence, and in the intraoperative conversions of surgical partial to complete tumor reponses are described.