Elastic and quasi-elastic light scattering and conductivity experiments have been performed on the supramolecular species [Ru{(mu-2,3-dpp)Ru[mu-2,3-dpp)Ru(bpy)(2)](2)}(3)](PF6)(20), 1, and [Os{(mu-2,3-dpp)Ru[(mu-2,3-dpp)-Ru(bpy)(2)](2)}(3)](PF6)(20), 2, in dilute fluid solution at room temperature (bpy = 2,2’-bipyridine; 2,3-dpp = 2,3-bis(2-pyridyl)pyrazine). Aggregation phenomena occur in fluid solution for 1 and 2 even at concentrations as low as 10(-6) M. The dimension of the aggregates at 298 K in a 10(-6) M acetonitrile solution is about 100 nm. The effects of ionic strength and solvent polarity on the aggregation are discussed. Intermolecular attractive interactions between the hydrophobic aromatic moieties of the supermolecules are likely at the basis of the aggregation process. The results obtained indicate that the nanometer-sized hyperbranched supermolecules investigated here can be considered as colloidal systems as far as the aggregation properties are concerned.