Despite developments in phonology over the last few decades, models of verbal working memory make reference to phoneme-sized phonological units, rather than to the features of which they are composed. This study investigates the influence on short-term retention of such features by comparing the serial recall of lists of syllables with varying types and levels of similarity in their onset consonants. Lists are (a) dissimilar (/fa-na-ga/) (b) acoustically similar (/pa-ta-ka/) or (c) articulatorily similar (/da-la-za/). When no overt articulation is required, we find no decrease in performance for articulatorily similar items as compared to the dissimilar list. However, we are able to show that acoustic similarity clearly impairs recall. It is only when participants recall the lists orally, that performance is impaired for both types of similar lists. These results have implications for accounts of the phonological similarity effect in particular and of verbal working memory in general. (Contains 5 figures and 1 table.)