The distribution of the oxides of nitrogen (NOx ) in the troposphere is the most critical parameter for understanding the photochemical component of the tropospheric ozone cycle. Recent studies by Liu et al. (1980) and Kley et al. (1981) have derived tropospheric NOx distributions that we believe are not consistent with most of the recent NOx measurements and that, consequently, may lead to an incorrent interpretation of the tropospheric ozone budget.