The dependence on urea (U) concentration of the solubility of benzene (B) and of the neutral iron(II) complex cis-[Fe(o-phenanthroline)₂(CN)₂](I) in aqueous solutions at 25 °C has been studied by u.v.–visible spectrophotometry. The increase in solubility of (I) over the range 0–4 mol dm^–3 urea corresponds to a single equilibrium constant β₂=[IU₂]/[I][U]²= 0.7 dm⁶ mol^–2, while the increase in solubility of B over the range 0–6 mol dm^–3 urea can be explained by the existence of two overlapping equilibria with constants K₁=[BU]/[B][U]= 0.03 dm³ mol^–1 and K₂=[BU₂]/[BU][U]= 0.3 dm³ mol^–1. Evaluation of the published data of Wetlaufer et al.(J. Am. Chem. Soc., 1964, 86, 508) shows that the urea-dependent solubility of butane in water at 25 °C also corresponds to the existence of two analogous equilibria. The observation of equilibria with simple stoichiometries and with solute-dependent equilibrium constants indicates that urea exerts its solubilising effect directly through the formation of specific adducts with the solute and not indirectly by disrupting the structure of the solvent.