This report addresses issues that have been raised recently about the measurements of reactive odd nitrogen and, in particular, those measurements made as part of the NASA Global Tropospheric Experiment airborne field campaigns. The test results presented here demonstrate that it is unlikely that HNO3 mixing ratios are underestimated by large factors (i.e., by greater than 1.5-fold) during the Pacific Exploratory Mission-West A, Transport and Atmospheric Chemistry Near the Equator-Atlantic, and Pacific Exploratory Mission-West B field campaigns and that other mechanisms are needed to explain discrepancies between measured and modeled HNO3 mixing ratios. Results from NOy conversion efficiency studies indicate that potentially large artifacts may have affected the Georgia Institute of Technology measurements of total reactive odd nitrogen (NOy). Assessing the exact magnitude of these artifacts is hindered by a lack of knowledge of both tropospheric distributions of non-NOy forms of fixed nitrogen and the efficiency with which they were detected at the time of the NOy measurement. Indirectly, our results suggest that up to ppbv levels of non-NOy fixed nitrogen (e.g., NH3, HCN, and perhaps nitrogeneous sulfur compounds) may exist in some regions of the remote troposphere. ¿ 1998 American Geophysical Union