Abstract: A method for destroying harmful cells is provided, applicable in treating proliferative diseases. The cells are destroyed by a combined treatment with a chemiluminescent agent and with a ligand-photosensitizer conjugate. The chemiluminescent agent emits light on reacting with oxygen species present in situ, the conjugate binds to the cell through its ligand and is activated by the emitted light, thereby destroying the cell. The method is demonstrated on a conjugate of transferrin-hematoporphyrin, which destroys cancerous cells in the presence of luminol.