Measurements of the root hydraulic conductance (L0) of roots of Arabidopsis thaliana were carried out and the results were compared with the expression of aquaporins present in the plasma membrane of A. thaliana. L0 of plants treated with different NaCl concentrations was progressively reduced as NaCl concentration was increased compared to control plants. Also, L0 of plants treated with 60 mmol/L NaCl for different lengths of time was measured. Variations during the light period were seen, but only for the controls. A good correlation between mRNA expression and L0 was observed in both experiments. Control plants and plants treated with 60 mmol/L NaCl were incubated with Hg and then with DTT. For these plants, L0 and cell-to-cell pathway contributions to root water transport were determined. These results revealed that in control plants most water movement occurs via the cell-to-cell pathway, thus implying aquaporin involvement. But, in NaCl-stressed plants, the Hg-sensitive cell-to-cell pathway could be inhibited already by the effect of NaCl on water channels. Therefore, short periods of NaCl application to Arabidopsis plants are characterised by decreases in the L0 of roots, and are related to down-regulation of the expression of the PIP aquaporins. This finding indicates that the well known effect of salinity on L0 could involve regulation of aquaporin expression.