New photodynamic, topically-applicable medicaments and certain medical uses of such photodynamic medicaments for treatment of human or animal tissue are described, wherein a primary active component of such medicaments is a halogenated xanthene. The halogenated xanthenes constitute a family of potent photosensitizers that become photoactivated upon illumination of the treatment site with visible wavelengths of light. In preferred embodiments, such medicaments are used for treatment of a variety of conditions affecting the skin and related organs; the mouth and digestive tract and related organs; the urinary and reproductive tracts and related organs; the respiratory tract and related organs; various other internal or external tissue surfaces, such as tissue surfaces exposed during surgery; and for treatment of a variety of conditions related to microbial or parasitic infection. In another preferred embodiment, such medicaments are produced in various formulations including liquid, semisolid or aerosol delivery vehicles.