This book contains the contributions of the participants to the International Symposium on Porphyrins in Tumor Phototherapy held in Bruzzano (Milano), Italy on May 26-28, 1983. The contributions are written as extended papers to provide a broad and representative coverage of the use of porphyrins in tumor phototherapy and diagnosis. In the last few years, this technique has received increasing interest for its potential applications in clinical oncology. In fact, 1,500 patients have been already treated by this therapy which has been tested in more than 100 clinical centres. Among the reported cases, a significant therapeutic effectiveness was found in some early stage cancers of lung, esophagus and stomach. The development of *this therapy requires interdisciplinary studies from such diverse fields as physics, chemistry, biology, pharmacology, and experimental and clinical oncology. The contents of the book reflect the character of this research and deal with all the problems, from fundamental to clinical, that still require to be analysed and understood for a better evaluation 'of the potential of this therapy. The first chapter of the book deals with photophysics ?;nd.