Trials have been conducted in the Western Mediterranean to confirm the excess attenuation of sound at frequencies between 200 Hz and 10 kHz. As sound propagation along the deep refracted path in the isothermal deep water of the Mediterranean is affected only by geometrical spreading and attenuation, it is possible to measure the attenuation separately for each frequency. The trials used explosive sound sources at different depths and at accurately determined ranges between 200 m and 30 km. Special care has been taken to separate the effects of finite amplitude from the attenuation and it is shown that the former are not responsible for the excess attenuation found at low frequencies. The authors have reported the analysis more thoroughly in SACLANTCEN Technical Report No. 156, “Sound Attenuation Between 200 Hz and 10 kHz.”