Development of early SEP components was studied, particularly in reference to the peak latency. Two factors were evaluated in the growing children. One was the correlation between latency and height and the other was the chronological change of latency divided by height (L/H). One hundred and four normal subjects ranging in age from 2 months to 26 years were studied in the awake state except those under 4 years of age. EEG was also examined in every case. The electrical stimulation was delivered every two seconds to the median nerve at wrist. Six components [P0(14), N1(18), P1(23), N2(30), P2(43), N3(60] were recognized in the contralateral Post-Rolandic area. Results were as follows: 1) Correlation between latency and height: Every peak latency was shortened in cases with height up to around 90-100 cm. With height over 100 cm, a highly significant correlation was observed in P0(14), and N1(18), but not in the other components. 2) Chronological change of L/H: The change of L/H revealed 3 different stages; by 1 year, by 3 to 4 years of age and thereafter. By 1 year, L/H was markedly shortened in every SEP component. Another rapid decrease occurred by 3 to 4 years of age. Thereafter, changes to reach the adult level were different from each other. L/H of P0(14) and N2(30) reached the adult level by around 9 years and N1(18) by around 11 years, P1(23) by around 12 years of age. While L/H of P2(43) and N3(60), more variable, still showed a significant difference from that of the adult level.(ABSTRACT TRUNCATED AT 250 WORDS)