AbstractCysteic acid and methionine sulphone were measured in soil hydrolysates by ion exchange chromatography, after pretreatment of the soil with performic acid. In four mineral soils these amino acids accounted for 19‐31% of the carbon‐bonded sulphur measured by difference between total organic sulphur and total organic sulphate, but only 8% in a peat. When carbon‐bonded sulphur is measured directly by reduction with Raney‐Nickel, however, the amounts are lower, and cysteic acid and methionine sulphone together account for 80‐100% of the values for the mineral soils and 50% of that for the peat. It seems therefore that Raney‐Nickel reduces only a fraction of the carbon‐bonded sulphur consisting mainly of amino