Hearing thresholds were established in preterm and term newborn infants by auditory brainstem responses in the first week of life. The presence of wave V was the criterion for threshold sensitivity in infants considered neurologically optimal on the basis of stringent clinical criteria and sequential ultrasound examination. The hearing threshold was found to be at 40 dB in preterm infants between 28 and 34 weeks gestational age, at 30 dB in infants between 35 and 38 weeks, and below 20 dB in term infants. This study confirms that the thresholds of newborn infants diminish with increasing age, and there is no apparent difference whether maturation occurs inside or outside the uterus. The data should provide a baseline for objective and quantitative assessment of hearing loss early in the neonatal period.