Drought strongly affects cereal yield in several regions of the world. Plant growth and plant water status in response to soil water deficit play an important role in tolerance to drought and in yield stability. In order to investigate the relationship between plant growth and water relations, 187 barley (Hordeum vulgare L.) recombinant inbred lines from a cross between two Mediterranean varieties, Tadmor and Er/Apm, were studied in a growth chamber for RWC, number of leaves on the main tiller (NL), number of tillers (NT) and total shoot fresh and dry biomass (TSFM and TSDM). Measurements were made at the beginning of tillering on well watered plants and at a soil moisture content of 14% of field capacity. A negative phenotypic correlation between RWC and growth parameters was obtained in both treatments. Under water stress, a negative genetic correlation was also found between the same characters. QTLs involved in RWC, NL and TSFM variation were positioned on a RFLP-RAPD genetic map. Different DNA regions involved in constitutive and water stress responses were detected. In the stress treatment, one region on chromosome 1 was involved in RWC and NL variation giving a genetic basis to the phenotypic correlations found. Separated map positions were also found for RWC and NL. Epistatic interactions between several QTLs and between QTLs and other markers were detected only in the water stress treatment, suggesting that some chromosomal regions might be involved in the regulation of the expression of the traits under water stress. This work suggested that even if some parameters are strongly correlated, finding QTLs for only one trait is not sufficient to detect all the candidate regions which might be involved in the control of the correlated traits. The results of localization and co-localization of QTLs are physiologically interpreted.