IN adults, neural networks for phonological processing distinct from those involved in acoustical processing are located in the left temporal lobe. We now report that by the age of 3 months, infants display phonological processing devices analogous to those found in adults. Within a stream of identical syllables, acoustic deviants were introduced, either crossing a phonetic boundary or remaining within the same category. Event-related potentials were recorded using a 64-electrode net. Although the acoustical change was of similar amplitude in the two deviants, the electrophysiological response was larger for a phonological change and involved a more posterior and dorsal temporal region than for an acoustical change. These results demonstrate that infants, like adults, already possess a dedicated neuronal network for phonetic processing.