Two hybrids (1 and 2) originating from a cross between maize and gamagrass (Tripsacum dactyloides L.) were tested for salinity sensitivity, measured as the reduction in shoot dry weight of plants grown for one month in the range 50-300 mM NaCl, relative to plants grown in the absence of salt. The maternal parental maize line V182 (2n = 4x = 40Zm) and two forage sorghum species were included for comparison. Hybrid 1 (2n = 39; 30Zm + 9Td) and Hybrid 2 (2n = 46; 10Zm+36Td) showed much less biomass reduction at 150 mM and 250mM NaCl, respectively, compared to the moderately salt tolerant parental maize line and more salt sensitive forage sorghum (Sorghum bicolor L. Moench.) and sudangrass (S. sudanese Staph.) cultivars at the same levels. Na+ accumulation in extract of leaves in both hybrids was very low, 7-8-fold lower than in the parental maize and in the growth solutions. It was concluded that the higher salinity tolerance of the two hybrids is attributable to a highly efficient Na+ exclusion mechanism. These results can explain our previous findings that both hybrids produced 11- to 16-fold more forage biomass compared to the parental maize line in a field trial on moderately saline soil.