Infants' ability to rapidly extract properties of language-like systems during brief laboratory exposures has been taken as evidence about the innate linguistic state of humans. However, previous studies have focused on structural properties that are not central to descriptions of natural language. In the current study, infants were exposed to 3- and 5-syllable words from one of the two artificial languages that employed the same stress assignment constraints found in natural languages. Infants were able to generalize beyond the stress patterns encountered during familiarization to new patterns reflecting the same constraints. The results suggest that infants are able to rapidly extract the types of structural information required for human language.