Photoconductivity of a series of perylene tetracarboxyl-dimides has been studied by delayed-collection-field and electric field induced fluorescence quenching techniques. It has been shown that these materials exhibit both extrinsic (impurity controlled) and intrinsic carrier generation originating from the first excited singlet state. Perylene tetracarboxyl-diimides are photoactive in the visible spectral range and their carrier generation efficiencies compare well with generation efficiencies in the best known organic photoconductors. This makes them suitable for xerographic applications using visible light.