This program is directed towards development of a novel and potentially very effective means of treating certain types of malignant tumors by means of in vivo application of the photodynamic effect. Hematoporphyrin and certain other dyes are injected and allowed to specifically accumulate in the tumors. The dyes are subsequently activated by means of visible, red light resulting in specific destruction of the tumors. Preclinical animal studies as well as a preliminary clinical trial has indicated very encouraging results may be obtained with good expectation of cure in some cases. We plan to define the scope, limitations and mechanisms of this method, study several dyes and various light sources for activation, e.g. conventional light sources and lasers. In addition we will study this novel technique as adjuvant or combination with other modalities.