A group of hydro-monobenzoporphyrins "green porphyrins" (Gp) having absorption maxima in the range of 670-780 nanometers is useful in treating disorders or conditions which are subject to hematoporphyrin derivative (HPD) treatment in the presence of light, or in treating virus, cells and tissues generally to destroy unwanted targets. The use of the Gp of the invention permits the irradiation for therapy to use wavelengths other than those absorbed by blood. The Gp of the invention may also be conjugated to ligands specific for receptor or to specific immunoglobulins or fragments thereof to target specific tissues or cells for the radiation treatment. Use of these materials permits lower levels of drug to be used, thus preventing side reactions which might destroy normal tissues.