It has been claimed that speakers distinguish between phonemically-identical initial syllables that differ in morphological structure, but the phonetic details are poorly understood. Five female SSBE speakers read scripted dialogues containing words with such syllables, half with true prefixes (Pr) e.g. mistimes, displease, and half with pseudoprefixes(PsPr) e.g. mistakes, displays. Each word occurred both with nuclear stress and in postnuclear position. Pr words were longer up to voicing onset in the second syllable and had longer vowel and VOT, and shorter [s] than PsPr words. In nuclear mis- words, the average amplitude of the burst + aspiration was higher in Pr than PsPr words. Implications for models of morphological decomposition are discussed.