Conjugate are formed by covalently linking a target-specific compound to pyropheophorbide compound which conjugated are injected into a host and accumulate in tumor tissue to a higher degree than surrounding normal tissues. When the pyropheophorbide compound component of the conjugate is exposed to a particular wavelength of light the compound becomes cytotoxic destroying the tumor or diseased tissue without causing irreversible normal tissue damage. The pyropheophorbide compounds have been shown to have a variety of characteristics when used in photodynamic therapy. These characteristics are further improved when the compounds are bound to a target specific component such as a ligand capable of binding to a specific cellular receptor (e.g. growth hormones and growth factors) or an antibody capable of binding to a particular antigen.