The possible significance of the compartmentation of major solutes between cytoplasm and vacuole is described. The barley cultivars appear to have a restricted ability, by comparison with S. × townsendii, to exploit Na+ and Cl- as major vacuolar ions and contributors to osmotic adjustment. They also appear less able to maintain a basal K- supply in the presence of Na+. The basal K+ supply to the shoot is interpreted as a requirement for a minimal cytoplasmic K+ concentration. The role of glycinebetaine and proline as cytoplasmic osmotic effectors is discussed. It is concluded that, in these hydroponic experiments, the synthesis of glycinebetaine and proline is not a limitation on the salt tolerance of these species.