This paper presents nighttime measurements of NO2 and HNO3 taken by the LIMS experiment aboard the NIMBUS 7 satellite. Measurements are shown as latitude-altitude distributions for December 1978 and March 1979. It is contended that the nighttime sum of NO2 and HNO3 represents a reasonable lower-limit estimate of the stratospheric NOx (NO2+NO +HNO3+NO3 +2xN2O5 +HNO4+HNO2 +ClNO3). The distributions of the sum of NO2 and HNO3 which are presented are free of assumptions about the stratospheric photochemical system and do not depend upon the use of models. Results show that the measured sum of nighttime NO2 and HNO3 is as high as 22.5¿4 ppbv and suggest that atmospheric NOx levels may be as high as 26¿4.5 ppbv at 37 km. This is substantially larger than most calculated NOx levels. The implication of these results is that the stratosphere is significantly less sensitive to large chlorine injections than recent calculations suggest.