The basic speech unit (phoneme or syllable) problem was investigated with the primed matching task. In primed matching, subjects have to decide whether the elements of stimulus pairs are the same or different. The prime should facilitate matching in as far as its representation is similar to the stimuli to be matched. If stimulus representations generate graded structure, with stimulus instances being more or less prototypical for the category, priming should interact with prototypicality because prototypical instances are more similar to the activated category than are low-prototypical instances. Rosch (1975a, 1975b) showed that, by varying the matching criterion (matching for physical identity or for belonging to the same category), the specific patterns of the priming x prototypicality interaction could differentiate perceptually based from abstract categories. By testing this pattern for phoneme and syllable categories, the abstraction level of these categories can be studied. After finding reliable prototypicality effects for both phoneme and syllable categories (Experiments 1 and 2), primed phoneme matching (Experiments 3 and 4) and primed syllable matching (Experiments 5 and 6) were used under both physical identity instructions and same-category instructions. The results make clear that phoneme categories are represented on the basis of perceptual information, whereas syllable representations are more abstract. The phoneme category can thus be identified as the basic speech unit. Implications for phoneme and syllable representation are discussed.