This letter reports high-pressure liquid chromatography (HPLC) measurements of H2O2 and organic hydroperoxides in cloud- and rain-water. Observations were conducted on the Kleiner Feldberg (Germany) from late October to late November 1995, within the FELDEX-campaign. It was the first campaign ever in which organic peroxides were determined in cloud-water. H2O2 was found with concentrations of <0.008-3 19 &mgr;mol⋅l-1. Hydroxymethyl hydroperoxide (HOCH2OOH, HMHP) and 1-hydroxyethyl hydroperoxide (CH3CH(OH)OOH 1-HEHP) were observed with concentrations in the range of <0.008--1.0 &mgr;mol⋅l-1 (HMHP) and <0.008--0.28 &mgr;mol⋅l-1 (1-HEHP). The ratio of the sum of organic peroxides over the total amount of peroxides (H2O2+organic peroxides) was 0--81%. The concentrations of S(IV) and H2O2 in the samples were anticorrelated. The results indicate that organic peroxides such as HMHP and 1-HEHP, should be included into modelling studies of the aqueous phase oxidation of S(IV). ¿ American Geophysical Union 1996