Absolute intensity measurements of the (8, 6) OH band obtained during 10 flights of the December 1969 NASA Auroral Airborne Expedition are presented. Nightglow intensities higher by a factor of 2 than the usual values are recorded during flights 8, 14, 15. The OH variations are compared with the evolution of the green line and O2(1Δg) emissions measured by other experimenters on board the aircraft. Before sunrise twilight variations of OH down to a solar depression angle of 5¿ show a rapid decrease. A theoretical prediction of the OH, O i 5577 ¿, and O2(1Δg) emissions measured by other experimenters on board the aircraft. Before sunrise the twilight variations of OH down to a solar depression angle of 5¿ show a rapid decrease. A theoretical prediction of the OH, O i 5577 ¿, and O2(1Δg) emissions is evaluated by means of an extensive time-dependent oxygen-hydrogen model of the 25- to 150-km region. Nighttime variations of the emissions may be reproduced if modifications of the dynamic regime are introduoed into the model.