Tone screening was performed in 14391 schoolchildren at three different age-levels, 7, 10, 13 years in grades 1, 4 and 7, and was carried out in 1977, 1978 and 1979. A 4 kHz dip greater than 20 dB was found in 331 (2.3%) of the children; 241 (1.7%) were boys and 98 (0.6%) were girls. The 4 kHz dip was unilateral in 230 (1.6%) and bilateral in 109 children (0.7%). The number of children with the 4 kHz dip increased with age. At the 13-year level it was found in 125 (4.7%) boys and 37 (1.5%) girls. The magnitude of the dip increased with age both in frequency range and intensity. At the 13-year level two and more frequencies were affected in 27 (0.5%) and hearing thresholds of 40 dB and worse were found in 47 (0.9%) of the children. Causes of noise could be established in 210 (63%) of 331 children. Most important noise causes were in the following order: motor vehicles, including tractors, fire-arms and crackers. In a small number, loud music could have been the cause of the 4 kHz dip. A hearing conservation program against noise has been instituted for children, parents, teachers and school nurses. Further studies will show if this program is effective.