AbstractA sensitive method has been developed for the simultaneous determination of S‐adenosyl‐L‐homocysteine (SAH) and S‐adenosyl‐L‐methionine (SAM) in a variety of plant tissues. Samples were extracted in acid and the extracts cleaned up and concentrated by a combination of partitioning with diethyl ether and cation exchange chromatography using phosphocellulose paper. After elution from the phosphocellulose paper with a minimal volume of 6M HCI, SAM and SAH were quantified by ion‐pair reversed phase high performance liquid chromatography with UV detection at 257 nm. Recoveries were monitored using a spike of [14C]‐SAM and were typically between 30 and 40%. In alfalfa, peas and maize the levels of SAM exceeded those of SAH, and in peas levels of SAM were higher in young roots and shoots than in older tissues. When alfalfa cell cultures were treated with a fungal elicitor preparation, the levels of SAM and SAH increased approximately two‐fold over a 12 h period