The equilibrium solubility of propranolol hydrochloride in aqueous binary mixtures of 1,4-dioxane (D), acetonitrile (ACN), polyethylene glycol 400 (PEG), propylene glycol (PG), or methanol (MeOH), at T = 298.15 K was determined. In all cases the maximum solubility values expressed in molarity (mol.dm(-3)) in a mixture instead of neat water were obtained, while the lowest drug solubility values in the neat cosolvents were obtained. Otherwise, if the maximum mole fraction solubility obtained in every cosolvent system is considered, the following order is obtained: ACN + W > D + W > MeOH + W > PEG + W > PG + W; whereas, if the molarity scale is considered the maximum solubility decreases in the order: ACN + W > MeOH + W > D + W > PG +W > PEG + W. In a quantitative way the drug solubility expressed in mole fraction varies from 1.77 x 10(-4) in neat 1,4-dioxane to 2.95 x 10(-2) in the mixture with 0.50 in mass fraction of acetonitrile. A correlation of the solubility data obtained was made by means of the modified NIBS/R-K model; thus, regressions in second and third order were obtained according the cosolvent system. Otherwise, apparent specific volumes at saturation (phi(sp)(V)) in all the mixtures were also calculated; in particular, a phi(sp)(V) mean value of 0.837 cm(3).g(-1) was obtained.