Previous experimental studies in speech perception have concluded that the syllable is not a prelexical segmentation unit for English speakers. The set of experiments reported here applied the attentional phoneme monitoring task of Pallier, Sebastian-Galles, Felguera, Christophe, \& Mehler (1993) to American English and demonstrated a robust effect of syllable structure when second-syllable stress words were used, but no such effect with first-syllable stress words. We hypothesize that aspects of syllable structure related to word stress are an important factor in the detection of syllabic effects in English.