Recent experiments have shown that placing dissimilar items on lists of phonologically similar items enhances accuracy of ordered recall of the dissimilar items [Farrell, S., & Lewandowsky, S. (2003). Dissimilar items benefit from phonological similarity in serial recall. "Journal of Experimental Psychology: Learning, Memory, and Cognition," 29, 838-849.]. Two explanations have been offered for this effect: an encoding explanation, in which items similar to current memory contents are given less encoding weight and offer less competition for recall; and a retrieval explanation, which suggests that the long-term similarity structure of the items leads to dissimilar items being more distinct on mixed lists. These theories are compared in an experiment in which a filled delay was introduced between study and test. Simulations show the prominent enhancing effects of similarity after a delay are captured by a model that assumes encoding is sensitive to the similarity of items to other list items [Farrell, S., & Lewandowsky, S. (2002). An endogenous distributed model of ordering in serial recall. "Psychonomic Bulletin & Review," 9, 59-79.], but are not handled by a retrieval model [the Start-End Model; Henson, R. N. A. (1998). Short-term memory for serial order: the Start-End Model. "Cognitive Psychology," 36, 73-137.].