This study investigated the maturational pattern of the cortical somatosensory evoked potential (SEP) in the preterm period. SEPs were recorded in 22 preterm neonates (27-32 weeks gestational age (g.a.), mean age 28.4 weeks g.a.; total of 46 studies). The infants were first tested at an average of 5 days. At birth, all of the infants had normal neurological examinations and normal cranial ultrasounds. On follow-up the infants were assessed regularly by a multidisciplinary team and all those included in this series, at follow-up periods of 6-25 months corrected age (mean 14.8 months), had normal neuro-developmental examinations. SEPs were recorded in all of the infants. The waveform consisted of triphasic positive, negative components (at 75 ms, 125 ms and 178 ms, respectively at 27 weeks g.a.). Latencies of these components decreased rapidly over the preterm period, such that by 32 weeks g.a. they were at 41, 72 and 112 ms, respectively. There appeared to be no differences in the maturational changes as a function of gestational age at birth.