Measurements of NO, NOx (NO+NO2), O3, and CO are presented from seven aircraft flights made over the eastern Pacific Ocean and the southwestern United States in spring of 1984. The sampling region was characterized by large- and small-scale variability for all of the measurements, likely as a result of vigorous synoptic-scale meteorology and the influence of tropopause folds. Median values for NO, NOx, O3, and CO from the flights made over the ocean in the region of 5.8--7.6 km were 10 parts per trillion by volume (pptv), 32 pptv, 46 parts per billion by volume (ppbv) and 120 ppbv, respectively. Corresponding values from two flights made over the continent at similar altitudes were 16 pptv, 38 pptv, 42 ppbv, and 111 ppbv. There was a strong tendency for NO or NOx to be correlated positively with O3 and to be anticorrelated with dew-point/frost-point measurements. No significant overall correlation occurred between NOx and CO for the ocean data. The variability of NOx was such that regions of net destruction and regions of net production of O3 were sampled both over the ocean and over the continent. However, in the middle free troposphere over the ocean, net O3 destruction was predominant. ¿ American Geophysical Union 1989