The structure factor and pair correlation functions have been obtained for the 1.1 M NaCl aqueous solution at temperatures up to 500 degreesC and at a constant pressure of 1000 bar with the energy-dispersive x-ray diffraction technique. The data have been also obtained for the 0, 0,55, 1.1, and 2.2 M solutions in water at ambient conditions. Analysis of the structure functions and the pair correlation functions shows that the dissolving of NaCl in liquid and supercritical water greatly affects its structure, decreasing, in particular, the probability of hydrogen bonding. At the same time, unusual behavior near the critical isotherm previously found for pure water can also be observed in the NaCl solution. (C) 2001 Elsevier Science B.V. All rights reserved.