The present study investigates infants’ sensitivity to word boundaries in fluent speech contexts. Using the headturn preference procedure, the first experiment demonstrated that 101/2-month-old American infants listened significantly longer to passages in which artificial 1-s pauses were inserted at word boundaries, as opposed to between syllables within words. A second experiment examined the possibility that word-stress patterns affect infants’ sensitivity to word boundaries in fluent speech. New groups of 101/2-month-olds were tested on new sets of passages. One group received passages with pauses at word boundaries or within words for words having a strong-weak (SW) stress pattern. Another group received similarly arranged passages but the pauses involved words having a weak-strong (WS) pattern. If infants use the onsets of strong syllables as cues to word onsets, they might be expected to prefer between-word pauses in the SW passages but within-word pauses in the WS passages, In fact, in both cases infants listened significantly longer to passages with between-word pauses. These results suggest that infants at this age may not rely heavily on word-stress patterns in locating word boundaries in fluent speech. [Work supported by NICHD and NIDCD.]