This invention relates to oligonucleotide targeting agents and their use in the treatment of diseased cells by selective photochemotherapy (PCT). PCT is a method of treating human diseases and disorders, bacteriological indications and other pathological conditions. PCT is based on the topical or systemic application of a photosensitizing agent, a precursor or pro-drug thereof, which preferentially accumulates in the target tissue. Irradiation of the photosensitizing agent located in the target. tissue with electromagnetic radiation of an appropriate wavelength and the interaction of the thus excited photosensitive moiety with oxygen leads to tissue damage and destruction of the irradiated areas.