An electrostatographic printer has a process unit adapted to be removably mounted in a main assembly of an electrostatographic reproducing machine, the process unit including a developement apparatus at which an electrostatic latent image is developed on an imaging member, and a transfer device which causes a developed toner image to be transferred from the moving imaging member to a copy sheet. The development apparatus is contained within a housing of an electrically insulating material, and comprises conductive means adjacent the exit portion of the development apparatus, i.e. the portion from which the imaging member emerges as it moves towards the transfer device. The conductive means includes a conductive coating on the exit portion of the developer housing, and a conductive seal member through which an electrical discharge path is provided. This reduces the tendency of debris to accumulate in the region of the exit portion, and prevents any debris which does accumulate from building up a charge (which would have detrimental effects on the developed image).