The development of components of VEP was studied in 150 infants and children between 2 weeks and 9 years of age participated as subjects. Ten adult subjects, 25 to 35 years of age were also studied. The results indicated that the VEP had a simple wave form, consisting of only a slowly rising positive wave to 140', 70' and 35' checks from infants of 2 to 8 weeks following birth. P1 wave appeared in response to 17.5' check stimulus at 10 weeks following birth. The latencies of P1 components shortened dramatically from infants of 2 to 4 months and the latencies of low spatial frequencies (140' and 70' checks) from infants at 4 months of age reached adult level but P1 latency of medium spatial frequency (35' check) did not reach adult level until age of 4 years. The latency of P1 component of high spatial frequency was matured by the end of 9 years of age. The development of P1 waves from both eyes was parallel in normal infants and children. The amplitudes N1P1 and P1N2 from infants and children with 2 months to 9 years were not affected by the age and significantly higher than those of adults group by 2 to 3 factors. Based on the results of our research, three phases were found in the development of the visual function in infants and children. The first phase was up to 4 months after birth, and characterized by the maturation of the low spatial frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)