Atmospheric sulfuric acid inputs and leaching in a tropical and temperate forest are compared. In both cases, H+ is mostly removed in the forest canopy. The tropical forest appears to be accumulating SO42- whereas the temperate forest is near steady-state. The tropical soil has a high capacity permanently to retain sulfate, which is probably related to its high sesquioxide content. The high sesquioxide content of the tropical soil apparently renders it very resistant to leaching by atmospheric sulfuric acid inputs.