Gaseous peroxides were measured during the North Atlantic Regional Experiment (NARE) aboard the Department of Energy's Gulfstream G-1 aircraft in August 1993. Flights originated in Halifax, Nova Scotia and covered a region extending several hundred kilometers from the eastern edge of the North American continent. Total peroxide concentration was dominated by H2O2. Median H2O2 concentration for all flights was 2.5 parts per billion by volume (ppbv), with the highest concentrations observed in spatially extensive layers between 250 and 1750 m above sea level. In the clean free troposphere, H2O2 concentration correlates strongly with the product O3*H2O, consistent with our understanding of the formation mechanism. The median peroxide concentration was 4 ppbv in pollutant plumes, with excursions above 11 ppbv. The high concentration of H2O2 observed, and its covariance with concentrations of anthropogenic species such as O3, NOy, and aerosol particles is attributed to the aging of polluted air masses advected from the continent in stable layers. ¿ American Geophysical Union 1996