Background development in the insulative magnetic brush development system is studied. Data are presented on background development on the photoreceptor (PC) and paper. Background development on the PC is due almost entirely to wrong sign toneru. This wrong sign toner does not transfer to paper because, during the transfer step, Coulomb forces repel wrong sign toner from the paper. Background development on paper is due to right sign toner. This right sign toner has two sources. First, right sign toner develops onto the PC even in reverse bias and subsequently transfers to paper because the total force balance on toner during development has some probability of being in the direction of the PC. Second, the presence of wrong sign toner in a developer mix enhances the development of right sign toner onto the PC for at least three reasons: 1) the development of wrong sign toner on the PC leaves a space charge in the carrier beads that forces right sign toner to the PC, 2) net wrong sign doublets will develop and could be split apart during transfer, and 3) the toner-photoreceptor and toner-carrier adhesion distributions could be altered.