In an acoustico-vestibular follow-up investigation of 91 four- to six-year-old children with birth weight below 2000 g, the same incidence of sensorineural hearing loss (19%) was found in 54 children treated with kanamycin in the neonatal period as in a group of 37 infants not treated with kanamycin. When comparing a group of children treated with both kanamycin and incubator (54 children) with a group treated with incubator only (16 children), no definite signs of synergism between incubator noise and kanamycin were found. However, the 5 cases of moderate or severe hearing loss all belonged to the group treated with both incubator and kanamycin. These 5 children had more severe neonatal complications, especially apnea, cyanotic spells and hyperbilirubinemia, which may increase the severity of the hearing loss. Among 56 incubator treated children with normal hearing (ISO standards) 52% had an audiogram pattern suggesting minor noise-provoked cochlear lesions. Among 18 non-incubator treated children with normal hearing only one child (6%) had a similar pattern. It should be stressed, however, that these children had no clinical symptoms of hearing loss.