A study has been completed on auditory brain stem responses (ABR) in preterm and full-term newborn infants. We have drawn up a regression score for latencies of waves I and V and the I-V interval both at 80 dB and 60 dB stimulation in infants considered neurologically optimal using stringent criteria on both clinical and sequential ultrasound assessment. The 80 dB stimulus gave more consistent results with a narrower standard deviation. Hearing thresholds were difficult to establish with consistency in this population. A parallel study of a neurologically suboptimal population with transient neurological abnormality showed deviations in the ABRs from those of the optimal population. This data should provide a baseline for assessment of abnormal infants.