Audiograms were taken on 20 young men before and immediately after exposure to Fighter-6 ground running-up noise, and their course of recovery was followed. The sound levels at the engine hatch were 117-128 dB(A). The noise-induced temporary threshold shift was more than 13 dB. The maximum threshold shift occurred at 4 kHz. The shift in the low and speech frequencies recovers more rapidly and is completed in 30 min, whereas that in the high-frequency range recovers much more slowly, not returning to normal until 24 h later. High-frequency hearing loss is at risk in groundcrew. In order to prevent hearing damage, they ought to wear ear-protectors. We discovered that the V-shaped depression was not at 4 kHz but at 6 kHz. The former view concerning the pathogenesis of "4 kHz depression", therefore, is open to question. This interesting subject warrants further study.