Biomedical Applications of Lasers - Photodynamic therapy (PDT) as a new modality for cancer treatment is studied in solutions, in cell suspensions and in-vivo. - Photosensitizing drugs (porphyrins, porphycenes and phthalocyanines) are graded according to their efficiency to generate singlet oxygen, the phototoxic intermediary. Changes in the triplet lifetimes of the sensitizers are measured as a function of oxygen content in different environments. - Binding of photosensitizers to erythrocytes and to liposomes, differing in composition and surface charge, are studied by absorbance and fluorescence spectroscopy. - The efficiency of oxidative damage, induced by PDT in erythrocytes, liposomes and various tumor cell lines, is monitored electrochemically in real time by the depletion of ambient oxygen. - Structure-activity relationships for different photosensitizers are derived from the correlation between the efficiency of a sensitizer and its 3-dimensional structure. - Novel photosensitizers for PDT are evaluated in-vivo using the chick chorioallantoic membrane (CAM) model. Video microscopy in real time serves to monitor the entire process of tumor growth, DT and tumor regression. Computerized image analysis is used to quantify occlusion of blood vessels nourishing the tumors, and the morphological modifications associated with vasoconstriction, as well as the resulting tumor necrosis.