An investigation of the acoustic correlates of stress or accent in infant vocalizations was undertaken using five English‐ and five French‐learning participants at two developmental points, the onset of word use (10–13 months) and late in the single‐word period (14–19 months). A data base of 555 disyllabic utterances (words and babble) was digitized from naturalistic recordings and quantified acoustically by indices of duration, amplitude, and fundamental frequency (F0). Cluster analysis as well as the results of perceptual judgments (i.e., both a bottom‐up and a top‐down approach) revealed a developmental trend toward the adult prosodic system. In addition, acoustic comparisons of French and American infants at both developmental points revealed differences in their use of amplitude,F0, and duration to accent a syllable. The differences were traceable to the adult patterns for the respective adult languages. These results suggest that infants’ perceptual attunement to prosody in the prelinguistic period manifests itself in the beginnings of adultlike production as early as the onset of word use. [Work supported in part by the UK Economic and Social Research Council.]