According to the two-phase model of growth response to salt stress by Munns, there are two major physiological problems that may limit crop performance under saline conditions. In a first phase, osmotic problems reduce extension growth so that plants show stunted growth and look dark-green in color. In a second phase, ion toxicity develops and growth of sensitive plants is severely inhibited. Based on physiological knowledge, a breeding program was initiated to improve the salt resistance of maize. First, an efficiently Na+-excluding inbred line (NaExIl) was established that combines superior Na+ exclusion at the root surface with low Na+ root-to-shoot translocation relative to the parental hybrid Pioneer 3906. Second, out of 200 inbred lines 16 inbred lines were identified with increased osmotic resistance. Crossing of these inbred lines with NaExIl resulted in newly developed hybrids (SR hybrids) that showed significantly improved grain yield performance under saline conditions (EC = 10 dS m(-1)). Whereas osmotic adjustment, turgor, and cell-wall acidification are maintained in the newly developed SR hybrids, cell-wall extensibility still seems to limit extension growth. The newly developed SR hybrids are ideal tools to study physiological traits that may contribute to salt resistance of maize. (C) 2009 Elsevier Ireland Ltd. All rights reserved.