The development of visual evoked potential (VEP) was studied in guinea pigs as a function of age. Ten newborn guinea pigs from 3 litters were used, and experiments were carried out with the animals over an age span ranging from 1 to 90 days. Periodic recordings were obtained at 5 day intervals from the first up to the twentieth day after birth and at 30 day intervals from the thirtieth to ninetieth day after birth. The results were as follows: 1) The VEP comprised 7 peaks at the first day after birth, while after the fifth day it was composed of 9 peaks. 2) During the development of the guinea pigs, the latencies of VEP decreased. The reduction of the latencies of peak N2 amounted to about 25% from the first to the thirtieth day. 3) The amplitude of the initial negative spike increased from the first to the fifth day after birth, and decreased after the fifth day.