The SKα shift between the valences of sulfur has been used to determine by X‐ray spectrometry the two main forms of sulfur present in plant material, viz: oxidised S (S6+) and covalently bonded sulfur (Sc). S6+and Scwere shown to correlate closely with sulfate, as determined by reduction with hydriodic acid, and cysteine+methionine S, respectively. The method is rapid and reliable provided the X‐ray spectrometer is stable and has high reproducibility in goniometer setting. The use of S6+and Scis recommended as an alternative to chemical methods for assessing the sulfur status of crops and the sulfur amino acid content of diets.