Gender differences in resting pulmonary function are attributable to the smaller lung volumes in women relative to men. We sought to investigate whether the pattern of response in operational lung volumes during exercise is different between men and women of similar fitness levels. Breath-by-breath volume changes of the entire chest wall ( V(.)( CW)) and its rib cage ( V(.)( Rc)) and abdominal ( V(.)( Ab)) compartments were studied by optoelectronic plethysmography in 15 healthy subjects (10 men) who underwent a symptom-limited ( W (peak)) incremental bicycle test. The pattern of change in end-inspiratory and end-expiratory V(.)( CW) ( V(.)( CW,EI) and V(.)( CW,EE), respectively) did not differ between the sexes. With increasing workload the decrease in V(.)( CW,EE) was almost entirely attributable to a reduction in end-expiratory V(.)( Ab), whereas the increase in V(.)( CW,EI) was due to the increase in end-inspiratory V(.)( Rc) in both sexes. In men, at W (peak) tidal volume [ V(.)( T), 2.7 (0.2) l] and inspiratory capacity [IC, 3.4 (0.2) l] were significantly greater than in women [1.8 (0.2) and 2.6 (0.2) l, respectively]. However, after controlling for lung size using forced vital capacity (FVC) as a surrogate, the differences between men and women were eliminated [ V(.)( T) /FVC 49 (3) and 45 (3) respectively, and IC/FVC 63 (2) and 65 (3) respectively]. All data are presented as mean (SE). In both men and women the contribution of the rib cage compartment to V(.)( T) expansion was significantly greater than that of the abdominal compartment. We conclude that gender differences in operational lung volumes in response to progressive exercise are principally attributable to differences related to lung size, whereas compartmental chest wall kinematics do not differ among sexes.