This study describes the assessment of the auditory brainstem responses (ABR) in normal and abnormal preterm and full-term infants. Normal values for wave latencies, interpeak intervals, amplitudes, and amplitude ratios were established in 56 infants (gestational ages: 28-42 weeks) considered neurologically 'optimal' on stringent clinical and imaging criteria. Maturation curves for hearing thresholds were obtained in 42 of these infants. Thresholds were demonstrated at 40 dB between 28 and 34 weeks gestation, at 30 dB between 35 and 38 weeks, and below 20 dB in term infants. These thresholds are lower than previously reported. Curves of latency-intensity function were established in relation to gestational maturity in 54 infants and proved helpful in diagnosing various types of hearing deficit.