An improved gas phase sampler and a recently developed nonenzymatic measurement method for H2O2 and HOCH2OOH(HMHP) are described. The gas phase sampler is equipped with a surfaceless intake to alleviate heterogeneous loss of H2O2 in the sampling line. The nonenzymatic method makes use of the aqueous phase Fention reaction for H2O2 measurement and is capable of speciation between H2O2 and HMHP, using a dual channel technique. By adding a third channel employing the well-established method of p--hydroxyphenylacetic acid (POHPAA) and horseradish peroxidase for total peroxide measurement, it is possible to differentiate H2O2, HMHP, and other organic peroxides, if present. The measurement technique was successfully deployed in a field study at George L. Smith III State Park, Georgia (82¿20'W, 32¿30'N). Preliminary data analysis indicates that the measured total peroxides range from 0.4 to ~6 ppbv, depending on meteorological conditions, and that organic peroxides, mostly HMHP, constitute between 20 and 80% of the total peroxides. The work reported here represents the first continuous and real-time measurements for these peroxides in the atmosphere. ¿ American Geophysical Union 1993