We report quantitative measurement of heat generation in Au-nanoparticle colloidal solutions induced by radiofrequency (RF) electromagnetic waves (13.56 MHz; 25 W). The possible role of Au nanoparticles in RF heating was systematically investigated by separating the metal nanoparticles away from the colloidal solutions by centrifugation. Contrary to the previously made assumption in this field, it is found that Au nanoparticles do not contribute to RF energy absorption. The electrical conductivity measurement of the solutions with and without Au nanoparticles reveals that the Joule heating via ionic conduction in the electrolyte solutions is the dominant mechanism of RF-radiation-to-thermal conversion. (c) 2011 Elsevier Inc. All rights reserved.