The paper describes a series of measurements on solutions of sodium chloride in distilled water over the frequency ranges 0.95-13 and 690-4 320 Mc/s. The results are discussed in terms of the Debye-Falkenhagen theory of electrolytes and of the available data on the absorption band exhibited by water in the region of 10 000 Mc/s (wavelength 3 cm). A comparison is made with the published results on the electrical properties of sea-water—for frequencies up to 10 Mc/s—and deductions are made as to its probable behaviour at very high frequencies.