The Henry's law constants for aqueous solutions of hydrogen peroxide (H2O2) and hydroxymethyl hydroperoxide (HMHP) were measured for temperatures from 278 to 293 K at a pH of 2.1 to 2.4. A lower limit for the Henry's law constant of bis(hydroxymethyl)peroxide was obtained. At 288 K the Henry's law constant was determined for pH values from 2.2 to 6.4. The gas-phase peroxides were generated by passing humidified zero air through a porous tube immersed in a thermostated hydroperoxide solution. The temperature dependence of the Henry's law constant can be expressed as HL-1>=exp(A/T-B). The values of A are 7,514¿519 for H2O2 and 10,240¿913 for HMHP, and the values of B are 13.63¿0.11 for H2O2 and 20.03¿0.20 for HMHP. The dependence of the Henry's law constants as a function of pH was studied. ¿ American Geophysical Union 1992