Rabbits were exposed in a nearly closed compartment to complex air shock waves of long duration and low overpressure. Sevre lung injuries were obesrved at overpressures that, according to criteria applicable to simple waveforms, should have caused no primary lung injuriy. Pressure-time functions near the thorax and, in some cases, within the thorax, were recorded. The former functions were subjected to spectral analysis, and were also used for calculating with mathematical models the response of the thorax of man and rabbit, respectively. Recorded and calculated pressure-time functions in the lungs of the rabbits showed good agreement. The analysis indicates that the frequency spectrum of the waves and resonance effects in the thorax might have been factors of importance for the production of the lung injuries and, therefore, should be considered when estimating hazards to man from experiments performed with animals.