Lung volumes and quasi-static deflation volume-pressure relationships were measured in male golden hamsters anesthetized with pentobarbital. Volume was measured with a pressure plethysmograph, and pleural pressure was estimated by the use of a water-filled esophageal catheter. Mean body weight +/- SE was 122.3 +/-3.0 g, mean lung weight was 0.74 +/- 0.2 g or about 0.6% of body weight. Mean lung volume at 25 cmH2O transpulmonary pressure (TLC25) was 7.2 +/- 0.14 ml, 9.78 +/- 0.17 ml/g lung weight or 5.92 +/- 0.06 ml/100 g body weight. Mean functional residual capacity was 2.4 +/- 0.06 ml or 33.3% of TLC25. Mean vital capacity was 5.2 +/- 0.13 ml. Mean quasi-static compliance of lung was 0.63 +/- 0.03 ml/cmH2O. Chord compliance of chest wall between lung volumes of 1 and 4 ml above RV was 3.39 +/- 0.53 ml/cmH2O. At FRC, the chest wall recoiled inward, so that pleural pressure was positive (1.4 +/- 0.13 cmH2O) and the lung was resisting further collapse. The slope of the lung's deflation volume-pressure curve changed at FRC, ERV was small (0.36 +/- 0.03 ml), and RV was determined by complete airway closure. Thus the mechanisms determining FRC are unusual and include an influence of airway closure.