Growth, grain production, and physiological traits were evaluated for Hordeum marinum, Triticum aestivum (cv. Chinese Spring), and a H. marinum-T. aestivum amphiploid, when exposed to NaCl treatments in a nutrient solution. H. marinum was more salt tolerant than T. aestivum and the amphiploid was intermediate, both for vegetative growth and relative grain production. H. marinum, was best able to 'exclude' Na+ and Cl-, particularly at high external NaCl. At 300 mM NaCl, concentrations of Na+ (153 mu mol g(-1) dry mass) and Cl- (75 mu mol g(-1) dry mass) in the youngest fully-expanded leaf blade of H. marinum were, respectively, only 7% and 4% of those in T. aestivum; and in the amphiplolid the Na+ and Cl- concentrations were 39% and 36% of those in T. aestivum. Glycinebetaine and proline concentrations in the youngest fully-expanded leaf blade of plants exposed to 200 mM NaCl were highest in H. marinum, (128 and 60 mu mol g-1 dry mass, respectively), lowest in T. aestivum, (85 and 37 mu mol g(-1) dry mass), and intermediate in the amphiploid (108 and 54 mu mol g(-1) dry mass). Thus, salt tolerance of H. marinum was expressed in the H. marinum-T. aestivum amphiploid.