ABSTRACT: BACKGROUND: There are few in-flight studies of cognition-related cerebral oxygen status in helicopter pilots. METHODS: Four male helicopter pilots volunteered for nine sorties during visual flight in a BK117 and UH-60J. The pilots' pre-frontal oxy-hemoglobin (O2Hb) and deoxy-hemoglobin (HHb) concentration were continuously monitored from the right/left sections of the forehead using near-infrared spectrophotometers with a consideration of motion artifacts. RESULTS: The concentration of O2Hb progressively increased (13.98 mumol*L-1 as a maximum increased concentration) in both the right/left sections of the forehead from the basal level during the heightened cognitive demand of helicopter flight. There was comparatively little change (4.32 mumol*L-1 as a maximum increased concentration) in HHb concentration during measurement of helicopter flight. HHb changes were apparently not affected by a heightened cognitive demand of helicopter pilots. CONCLUSION: These results demonstrate that near-infrared spectroscopy, especially O2Hb measurements, provides a sensitive method for the monitoring of cognitive demand (maneuvers) in helicopter pilots.