The structure-sensitivity relationships of several series of bisazo pigments have been studied in bilayer xerographic devices using a common charge (hole) transporting layer (CTL). For a given bisazo pigment series, a correlation is found between the E0.5 value for each pigment and the Hammet constant σp. The data consistently show that neither electron-withdrawing substituents nor electron-releasing substituents promote high photosensitivity. Factors that influence the sensitivity of these pigments in devices, including photogeneration efficiency of the bisazo pigment in the charge generation layer (CGL), charge transfer efficiency from CGL to CTL, and mobility of the holes in CTL, have been considered. Because a common CTL is used and because a different substituent effect would have been observed if interfacial charge transfer were a factor, we conclude that the structure-sensitivity relationships are simply the effect of a substituent effect on the photogeneration efficiency of the pigment. Whereas impurity, particle size, and aggregation of the pigment are found to contribute little to the sensitivity variation, evidence is provided that the variation correlates to the crystallographic properties. Specifically, the photosensitivity is found to depend inversely on the crystallinity of the pigment. In view of the photogeneration mechanism, we postulate that the structure-sensitivity relationship originates from the surface area for the photogeneration process: the smaller the crystallite size, the larger the surface area, and consequently higher the photosensitivity.