In 37 healthy men aged 23-53 years the ratio of one-second and forced vital capacity of the lungs during forced inspiration and expiration FIV1/FIVC and FEV1/FEVC was recorded, (i.e. 0.901 as compared with MPa) a significantly higher value of FIV1/FIVC than of FEV1/FEVC was recorded, (i.e. 0.901 as compared with 0.857, p less than 0.05), at pressure of 0.4 MPA the reverse occurred: variable FIV1/FIVC was substantially smaller than FEV1/FEVC (0.635 vs. 0.731, p less than 0.01). The authors express the view that this phenomenon could be explained by the theory which assumes that the expiratory muscles in healthy subjects do not display during forced expiration their maximum strength and only under hyperbaric conditions when the stream resistance of the airways rises their strength is fully used. On the other hand, the maximal strength of the inspiratory muscles is involved already during normal pressure and thus a significant increase cannot occur under conditions of overpressure.