The use of porphyrins for localization and photodynamic therapy of neoplastic disease has been the topic of several international symposia, reviews and books during the preceeding five years. The literature on this topic has continued to grow, as have numbers of presentations at national and international meetings relating to photobiology, chemistry, and lasers. In this volume, it is the intention of the editor to provide both information on current research projects, and detailed methodology used in such investigations. A bibliography on the subjects of porphyrin localization and therapy is included. The manuscripts contained in this volume are based on reports given at a Porphyrin Photosensitization Workshop which was held in Philadel phia, July 6-7, 1984. This Workshop was supported by NIH grant CA 36746, together with funds from the Fogarty International Center. Authors were requested to update their contributions to provide a summary of progress to mid 1985. Manuscripts containing material not presented in Philadelphia are also included, notably a series of articles describ ing current clinical and pre-clinical results from China. Since the Philadelphia Workshop, a meeting was held in Alghero, Sardinia (May, 1985), and additional conferences are now being planned; this attests to the continued interest in photodynamic therapy involving porphyrin photo sensitization.