Transient evoked otoacoustic emissions (TEOEs) were recorded in a cohort study of preterm neonates in order to study their basic properties as a function of gestational age. Their main properties were: (1) TEOEs spectrum did not vary with age; it was analogous to those of full term; (2) there was no statistically significant variation of the TEOEs amplitude with age. The maturation of outer hair cell properties appears to be complete at a gestational age of 29 weeks. Because a number of infants at risk for hearing loss are preterm babies, screening for TEOEs has to be performed in the neonatal care unit. To improve the accuracy and efficiency of the test, screening should take place as close to hospital discharge as possible, with the optimum time at 35 gestational weeks.