Acoustic reflex thresholds (ART) were measured ipsilaterally in 20 neonates, 220 children with normal hearing and 56 children with sensorineural hearing loss, using a probe-tone frequency of 660 Hz. Middle-ear function was assessed with tympanometry (220 Hz probe tone) in all children. All the neonates had normal tympanograms and middle- ear pressure better than -- 1kPa, even a few hours after birth. The mean acoustic reflex threshold (ART) averaged over the frequency range 0.5-4 kHz was 85 dB HL, with standard deviations (SD) varying between 5 and 9 dB. With broad-band noise (BBN), the mean ART average was 57 dB HL with SD +/- 10 dB. Measurements of the ART on the children with normal-hearing and at an age of 1 month up to 5 years showed that the ARTs increased in relation to age. At 4 kHz the ARTs increased from an age of 2 months. At an age of one year 28% of 40 ears failed to manifest a reflex at the maximum testing level (90 dB HL). At frequencies 1.0 and 2.0 kHz the mean ART increased from 85 dB HL in neonates to 90 and 92 dB HL at an age of 5 years. The standard deviations in the different age groups varied between 4 and 9 dB for pure tones and 6-8 dB for BBN. Twenty (9%) of the 220 children with normal hearing had elevated ARTs by puretone stimuli and 19 by BBN. No reflexes could be elicited at 0.5 kHz and at 1.0 and 2.0 kHz the ARTs were abnormally elevated.(ABSTRACT TRUNCATED AT 250 WORDS)