The authors studied age-related correlations of auditory event-related potentials (ERPs) using the conventional 'oddball' paradigm and reaction time in 175 normal subjects, aged between four and 21 years. From four years, the latencies of N100, N200 and P300 in ERP progressively shortened until about 16 to 17 years, after which they reached adult level, but with a slight tendency to prolongation towards 20 years; there was no trend for amplitude changes. The reaction time was more rapid than that of P300 latency. These findings indicate that the cognitive function of children improves rapidly until 16 to 17 years. A reduced difference between P300 latency and reaction time with age implies additional progress in motor skill. Combining P300 latency and reaction-time studies may provide more detailed information for the evaluation of the development of cognitive function and motor skill.