Measurements of NO, NOx (NO+NO2), and NOy (NOx+2N2O5+NO3+HONO+HO2NO2+PAN+R-ONOx) were made in March 1983 between 200 and 12,000 m altitude on several flights in the Arctic and from Spitsbergen, Norway, to Cologne, West Germany. NO values were always below the detection limit (10 ppt):NOx values (determined with a FeSO4 converter) were high, ~600 ppt, in the boundary layer and generally decreased sharply with altitude, although distinct strata of high NOx were observed at altitudes up to 8000 m. NOy (measured with a 425¿C Mo converter) showed altitude profiles similar to NOx profiles with boundary layer values as high as 1500 ppt. Ratios of NOx to NOy were 0.81 near the surface and 0.46 at 6400 m, probably owing to higher levels of PAN or other organic compounds in the free troposphere. The possible global impact of high concentrations of reactive nitrogen compounds in the Arctic is discussed.