Performance on tests of source memory is typically based on recollection of contextual information associated with an item. However, recent neuroimaging results have suggested that the perirhinal cortex, a region thought to support familiarity-based item recognition, may support source attributions if source information is encoded as a feature of the relevant item (i.e., "unitized"). The authors hypothesized that familiarity may contribute to source memory performance if item and source information are unitized during encoding, whereas performance may rely more heavily on recollection if source information is encoded as an arbitrary contextual association. Three source recognition experiments examining receiver operating characteristics and response deadline performance indicated that familiarity makes a greater contribution to source memory if source and item information are unitized during encoding. These findings suggest that familiarity can contribute to source recognition and that its contribution depends critically on the way item and source information are initially processed.