Hydrogen peroxide (HP), methyl hydroperoxide and hydroxymethyl hydroperoxide were measured by a 3-channel fluorescence analyzer aboard the Department of Energy's Gulfstream aircraft, and at the Williams Tower site in Houston during the late summer of 2000. Flight paths included the highly industrialized ship channel as well as the heavily trafficked downtown area, principally at an altitude of 500 m. Median total hydroperoxide concentration was 5 ppbv above 1 km during morning flights. This abundance, consisting of 54% HP, may be viewed as a regional background. Total peroxide as high as 16 ppbv was recorded in plumes during afternoon flights; median total peroxide increased substantially between morning and afternoon flights (7.1 vs 3.7 ppbv). Peroxide loss was associated with increased sulfate in aerosol particles within power plant plumes, indicating that particle surface deposition contributed to peroxide loss. On August 26 and 29, we observed broad plumes of elevated O₃, aerosol particles and NO_z. Low-NO_x regions within plume were associated with elevated peroxides as well. At the Williams Tower site, total hydroperoxide concentrations reached maximum levels between 4.5 and 8.5 ppbv in the late afternoon. Because of the high abundance and unusual mix of hydrocarbon precursors, the identity and distribution of individual peroxides in this region merits further study.