Maturational changes in short latency somatosensory evoked responses (SERs) were studied in 18 healthy full-term newborns in the first week of life and consequently repeated at 2-3 and 6-7 months of age. Both median nerves were electrically stimulated individually and evoked responses were recorded at 3 levels: Erb's point (EP), second cervical vertebra (CII), and contralateral parietal scalp (C'c). In the neonatal period, results of 32 stimulated nerves were obtained in all cases at the EP and CII levels. At the parietal level, potentials were present in 85% of cases, absent in 9% and questionable in 6%. Parietal potentials were occasionally noted on one side only. Repeat examinations at 2-3 and 6-7 months of age demonstrated significant maturational changes in the SERs. These changes were most prominent in the neonatal period and 2 months of age. They included decreased interpeak latencies, increased amplitude and markedly diminished dispersion of parietal potentials. Minimal changes in wave form configuration and latency were noted at the EP and CII level. These findings most likely reflect myelination and increased synaptic efficiency predominantly in the central sensory pathway. The purpose of this investigation was to delineate a reliable technique for SERs in newborns and infants that could be applied both to research and clinical settings. Normative data were established in newborns and infants as this will help us in accurately differentiating a normal from an abnormal group of neonates and infants.