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The reaction of SO2, dissolved in cloud droplets, with atmospheric oxidants such as H2O2and ozone is thought to be an important pathway for the production of atmospheric sulphate, and may be significant in determining the pattern of acidic deposition over a region. Direct observation of in-cloud oxidation of SO2by these species, however, has proved extremely difficult. This is especially true for H2O2because the reaction is so rapid. We have used a new experimental design to investigate the dominant oxidation pathways of SO2in the conditions that occur in natural clouds. This involved modifying SO2levels in capping cloud on a peak in the northern Pennine hills of England by releasing SO2locally upwind and then measuring changes in cloud and air composition. Here we present initial results from an experiment performed on 12 December 1985. Under the conditions encountered it was found that sulphate production by both ozone and H2O2was negligible. The destruction of H2O2by reaction with SO2, however, was clearly demonstrated. By comparing H2O2in the presence and absence of released SO2, the rate of destruction was estimated and found to be comparable with that expected from laboratory measurements of the reaction rate constant, and our knowledge of the cloud physics.