Sulphate at concentrations of less than 30 mg 1–1 of sulphur is determined on the AutoAnalyzer by reduction to hydrogen sulphide, distillation of the latter and its subsequent colorimetric determination. The method has been found to be suitable for aqueous solutions of sulphate, digests of leaf samples and animal faeces, and extracts of soils; it is applicable to a wide range of agricultural, biological and industrial materials.