Demethylated CPZ metabolites are phototoxic to cells, as revealed by the NRU assay. Single cell electrophoresis (Comet Assay) confirms the photodamage to cellular DNA. DNA single strand breaks formation is observed on agarose gel electrophoresis. Photochemical and EPR studies support generation of aryl radicals by C-Cl cleavage. The aminoalkyl side chain of metabolites modulates the photo(geno)toxic potential.