A process for depositing magnetic toner material on electrostatic latent images formed on an image bearing surfaces includes the steps of conveying toner to the developing zone via a magnet roll having a shell and coaxial permanent magnet member rotating in the same directions. In the region of the developing zone, the toner is subjected to both an A.C. magnetic field and an applied A.C. electrical field so as to render the toner electroconductive. The A.C. electrical field has a peak voltage greater than the dark voltage of the latent image, but less than 3,200 volts, and a frequency greater than v/0.3 where v is the advancing speed of the image bearing surfaces in relation to the magnet roll.