We report on a new method, based on random laser emission, to investigate the formation of dimers in laser dye solutions. The single peak spectrum observed at low dye concentration evolves to a double peak spectrum as the concentration increases, and a simple analysis allow us to directly investigate the dimers bonding energy. Our samples were prepared with rhodamine laser dyes dissolved in ethanol, containing TiO2 nanoparticle scatterers. The laser dyes used in this experiment were Rhodamine 590, Rhodamine 610, Kiton Red 620, and Rhodamine 640. Our results are corroborated by theoretical and experimental data in the literature. (C) 2008 Elsevier B.V. All rights reserved.