SUMMARYSurface and subsurface samples of three tropical soils were examined with respect to their interaction with dilute solutions of sulphuric acid of pH 3. In calcareous clayey samples with a large cation exchange capacity the H+was replaced by an equivalent concentration of metal cations which remained in solution along with SO2‐4as counterion. In a coarse‐textured neutral soil with small cation exchange capacity, there was less chemical interaction and a major proportion of the H2SO4remained unchanged in the equilibrium solution. Another soil exhibited considerable ability to remove SO2‐4from solution and, therefore, the total ionic concentration was greatly reduced. Other samples showed behaviour which was intermediate to these three types.The ability to adsorb SO2‐4is one of the most important factors which determines the nature of the interaction of soil with dilute sulphuric acid. This ability was shown to be affected by the content of hydrous sesquioxides and organic matter in thes