Measurements of H2O2 in rainwater collected in Miami, Florida, and the Bahama Island area indicate the presence of H2O2 concentration levels ranging from (1--7)¿10-5 M. No systematic trends in H2O2 concentration were observed during an individual storm, in marked contrast to the behavior of other anions (e.g., 3->, 4->, and ->). The data suggest that a substantial fraction of the H2O2 found in precipitation is generated by aqueous-phase reactions within the cloudwater rather than via rainout and washout of gaseous H2O2.