Rice varieties Co39 and Moroberekan differ for leaf Na⁺ concentrations when grown at moderate salinity (100–150 mol m^–3 NaCl; 10 : 1 or 20 : 1 Na⁺ to Ca²⁺ ratio). Recombinant inbred lines (RILs) from a cross between them were used to map quantitative trait loci (QTL) under salt stress over several weeks. Two experiments (conducted with 170 and 96 RILs, and a linkage map of 126 RFLP markers) identified a major effect on QTL for leaf Na⁺ concentration and K⁺ : Na⁺ ratio on chromosome 1 in a region corresponding to 11.07–14.6 Mbp. No leaf Cl^– QTL were detected. In a third experiment, leaves and sheaths were harvested after 7 and 21 days at 100 mol m^–3 NaCl. The linkage map of chromosome 1 was improved by the addition of 28 microsatellite markers, which resolved distinct QTL for Na⁺ and K⁺ concentrations, and K⁺ : Na⁺ ratio. After 7 days’ stress, the most significant QTL were in the region of 11.56–12.66 Mbp. The highest Na⁺ concentrations were recorded in the sheaths. Na⁺ concentration QTL were detected for leaves, but not for sheaths. After 21 days’ stress, the region containing the most significant QTL extended to 11.07 Mbp in leaves and in sheaths. A QTL for the ratio of leaf Na⁺ to sheath Na⁺ concentrations was found at 11.39–12.39 Mbp. These findings suggest that multiple genes in this region are involved in the response to salinity, and their impact is dynamic according to stress duration, and leaf age and type.