The surface tension and density of distilled water, physiological solution and salt solutions of the DNA, irradiated by nonthermal coherent millimeter electromagnetic waves with the frequencies 64.5, 50.3, and 48.3 GHz are investigated. The measurements of test samples show that due to irradiation the surface tension does not change within the experimental error. The densities of physiological solution and the salt solutions of the DNA increase under irradiation at the frequencies 64.5 and 50.3 GHz, which coincide with the resonant frequencies of oscillations of molecular water structures.