The alveolar pressure was measured in 15 healthy men at different flow rates breathing without and with additional resistance from a stenosis (diameter 7 mm). Ventilation, breathing frequency, pulse rate, O2-uptake, and CO2-elimination were also measured during rest and during bicycle exercise. At rest, FRC and gas exchange were unaltered, while ventilation and breathing frequency little with the additional resistance. During work, however, the stenosis, caused increased O2-uptake and CO2-elimination and decreased ventilation and breathing frequency. The mean O2-consumption by the respiratory musculature necessary to overcome the airway resistance is 0.00042 ml/gcm.