Photodynamic therapy (PDT) has become an approved treatment for different types of cancer in many countries over the last few years. As an example one might mention PDT of the early stages of bronchial or esophageal cancer which have been treated with only about 20% recurrence being observed over several years of follow-up. The low degree of invasion of PDT, as compared to most alternative treatments as well as minimal sided effects, and good repeatability, all speak for this treatment modality. Improved and cheap screening procedures, that are now being developed for the early stage disease, will lead to a more frequent application of PDT for these indications. Detailed studies of PDT showed that certain dyes, after systematic or topical application, could be taken up more in neoplastic tissue as compared to the surrounding normal tissue in the clinical context, thus leading to 'selective' or at least partially selective destruction of the tumor following light application. This selectivity of uptake of certain compounds in hyperproliferative tissue, as well as the observation that PDT can lead to blood vessel stasis, suggested that photodynamic therapy might be worth trying in non-tumor disease. Some of the diseases associated with hyperproliferation and/or neovascularization which are being considered for PDT are listed in table I.