Photodynamic therapy (PDT) is a promising new treatment for cancer that has been recently accepted in the clinic. PDT involves the localization of a light-sensitive drug (photosensitizer) in the target tissue prior to illumination using an appropriate wavelength. Cytotoxic agents generated upon illumination trigger a cascade of biochemical responses that inactivate cancer cells either directly or through the induction of vascular stasis. These treatments are better tolerated as they destroy diseased tissue while leaving normal tissue intact. The haematoporphyrin derivative, Photofrin(R), has been approved in a number of European and Asian countries, as well as in North America. To enhance the potential of PDT and explore its application for other conditions, second-generation photosensitizers are being rigorously investigated.