Perceptual priming refers to the phenomenon whereby experience with a stimulus induces systematic changes in subsequent processing of that same stimulus. Looking at a face, for example, alters how that person's face is recognized when viewed subsequently, as indexed by increased accuracy or reduced response time. Perceptual priming can be disrupted by various stimulus transformations. Priming would be reduced, for example, if a very different image or view of the same face was initially presented, or if only the person's name was initially presented. Here, we measured event-related potentials (ERPs) associated with perceptual priming of faces. Participants first attempted to memorize 80 pre-experimentally unknown faces. The next day they viewed faces and judged each according to whether or not they remembered it from the learning session. Half of the faces were familiar (i.e., from the learning session) and half were unfamiliar. Each face was presented twice in the task; half of the initial face presentations were inverted and half were upright; all second presentations were upright. We observed a positive-going ERP modulation for second versus first presentations of familiar faces around 250 ms occipitally. This positivity was apparent only for faces presented upright both times. A similar topography was observed for second versus first presentations of unfamiliar faces. The sensitivity of this ERP modulation to the stimulus transformation from first to second presentation suggests that it reflects primed perceptual processing (i.e. structural encoding). This ERP modulation thus specifically indexes the time course of priming-induced changes in perceptual processing.