Background. In fighter aircraft positive pressure breathing is commonly used as part of the anti-G ensemble. To optimize G-protection and prevent overdistention of the lungs, increased airway pressure is balanced by applying a counter pressure to the chest. The aim of the study was to investigate the efficacy of chest counter-pressure. Methods. Three series of experiments were performed using the anti-G ensemble of the 39 Gripen aircraft (AGE-39). In the first series 12 subjects were exposed to 20 s G-time profiles up to 8.0 Gz. In the second series 9 subjects were exposed to 20 s profiles up to 9.0 Gz and simulated aerial combat maneuvers (SACM). Impairment of central and peripheral vision, arterial and airway pressures, pressure in the lower portion of the esophagus and chestwall distension were measured in series 1 and 2. In the third series, 6 subjects were exposed to 20 s profiles up to 7.0 Gz and esophageal pressure was measured in the upper thorax. In all series, two conditions were compared: with and without pressurized chest bladder. Results. During the 20 s profiles arterial and esophageal pressures, chest wall distension and visual impairment were of the same magnitude with and without pressurized chest bladder. Upper esophageal pressure was slightly higher with than without chest bladder. During SACM, time to exhaustion and the level of perceived exertion were similar with and without pressurized chest bladder. Summary. The results suggest that the chest counter-pressure can be removed from AGE-39 without diminishing G-tolerance or G-endurance or significantly increasing the risk of lung parenchyma disruption.