Nitric oxide (NO) and total reactive nitrogen (NOy) were measured at the NOAA Geophysical Monitoring for Climatic Change baseline site near Barrow, Alaska, during July--August 1988. Concentrations of NOy in air from the clean-air sector (45¿ to 130¿) range from non-detectable to 300 ppt (hourly-average), with a median value of 100 ppt. NO concentrations were generally less than the detection limit of 50 ppt and reach a maximum of 100 ppt. These levels are similar to those observed at other remote sites, and are lower than the two previous measurements of NOy and peroxyacetyl nitrate (PAN) in the Arctic during spring. A diurnal cycle in NOy concentrations was also observed, with maximum levels near local solar noon, and minima near midnight. The cause of this cycle is not known, but it may be due to (1) daytime ventilation of NOy-rich air to the surface each day combined with fog scrubbing or dry deposition at night or (2) biological production of NO. ¿ American Geophysical Union 1990