The altitude distribution of NO was measured between 12 and 33 km near 54 ¿N during the stratospheric warming of February, 1979. The NO mixing ratios were considerably smaller compared to summer conditions, especially below 23 km. The measurements are used to estimate the distribution of NO2 for comparison with ground-based column measurements and to show that during the warming NOx is at least a factor of two lower than is observed in summer at this latitude. This reduction in NOx is shown to be consistent with a larger fraction of odd-nitrogen existing as N2O5.