This study investigated whether acoustic input, in the form of infant-directed speech, influenced infants' segmenting of action sequences. Thirty-two 7.5- to 11.5-month-old infants were familiarized with video sequences made up of short action clips. Narration coincided with portions of the action stream to package certain pairs of clips together. At test, packaged and nonpackaged pairs of actions were presented side by side in silence. Narration heard during familiarization influenced how infants viewed the action units, such that at test, infants older than 9.5 months (but not younger) looked longer at the nonpackaged than the packaged action sequences. The role of infant-directed speech as well as other types of acoustic input in assisting infants' processing of action is discussed. (Contains 2 figures and 2 footnotes.)