The auditory brain stem response (ABR) of a single group of developing normal infants was examined longitudinally, from newborn through 6 months of age. A sufficiently broad range of stimulus variables was included to ensure that the auditory system was adequately sampled in order to demonstrate developmental principles. Findings indicate that there are no differences in wave V latency-intensity functions between infants and adults. For waves I, III, and V, absolute and interwave latency-repetition rate functions differ between infants and adults and undergo systematic changes throughout the first 6 months of life. The most dramatic ABR changes (between any two sequential test sessions in infants) occurred between the ages of newborn and 2 weeks, with less pronounced ABR changes beyond 2 weeks of age. The pattern of latency change for wave I was different from that for waves III and V. After 2 weeks of age, wave I latency was the same as the adult value at all repetition rates. In contrast, waves III and V were characterized by decreasing latency throughout the follow-up period. A curvilinear developmental model provided a satisfactory fit to ABR latency data.