The annual cycles of hydrogen peroxide (H2O2) and methylhydroperoxide (MHP) have been investigated at a remote site in Antarctica in order to study seasonal variations as well as chemical processes in the troposphere. The measurements have been performed from March 1997 to January 1998 and in February 1999 at the German Antarctic research station Neumayer which is located at 70°39S, 8°15W. The obtained time series for hydrogen peroxide and methylhydroperoxide in near-surface air represents the first all-year measurements in Antarctica and indicates clearly the occurrence of seasonal variations. During polar night mean values of 0.054 ± 0.046 ppbv (range <0.03 0.11 ppbv) for hydrogen peroxide and 0.089 ± 0.052 ppbv (range <0.05 0.14 ppbv) for methyl-hydroperoxide were detected. At the sunlit period higher mixing ratios were found, 0.20 ± 0.13 ppbv (range <0.03 0.91 ppbv) for hydrogen peroxide and 0.19 ± 0.10 ppbv (range <0.05 0.89 ppbv) for methylhydroperoxide. Occasional long range transport of air masses from mid-latitudes caused enhanced peroxide concentrations at polar night. During the period of stratospheric ozone depletion we observed peroxide mixing ratios comparable to typical winter levels.