Abstract: This invention provides novel compounds for therapy of tumors susceptible to necrosis when an appropriate compound is administered followed by illumination with light of a wavelength absorbed by the compound, the compounds being dihydro porphyrins of the formula, or the corresponding tetra-hydro porphyrins: ##STR1## where n=1 to 3 and each substituent R, the same or different and at the same or different position in its respective substituent phenyl ring, is an hydroxy group.

Abstract: This invention provides novel compounds for therapy of tumors susceptible to necrosis when an appropriate compound is administered followed by illumination with light of a wavelength absorbed by the compound, the compounds being dihydro porphyrins of the formula, or the corresponding tetra-hydro prophyrins: ##STR1## where n=1 to 3 and each substitutent R, the same or different and at the same or different position in its respective substituent phenyl ring, is an hydroxy group.

Abstract: This invention provides for therapy of tumours susceptible to necrosis by a porphyrin when an appropriate porphyrin compound is administered to locate in the tumor followed by illumination with light of a wavelength absorbed by the compound, making use of meso-porphyrins of the formula: ##STR1## where n=1 to 3 and each substitutent R, the same or different and at the same or different position in its respective substituent phenyl ring or other aromatic group replacing that ring, is an hydroxy, amino or sulphydryl group, by association of said meso-porphyrins with a suitable pharmaceutical diluent or carrier.