This study was based on a population of 118 RILs (IR55178) from the cross between IR4630 and IR15324 advanced by single seed descent to F6 in greenhouses at the University of Sussex and at La Mayora, an Institute of the Consejo Superior de Investigaciones Cientificas in southern Spain. Plants were bagged to prevent cross pollination. Heritability studies were conducted by regression of F4 on F3 means using a random subsample of 44 lines. Each of the RILs was bulked at F6 at the IRRI and used for phenotyping and mapping. Both parents are modern, elite breeding lines and demonstrated good heritability of the traits of sodium and potassium transport. The genetic map was constructed with AFLP markers and anchored with microsatellite and RFLP markers.