WATER COSOLVENT MIXTURES.Extended Hildebrand Solubility Approach (EHSA) developed by Martin et al. was applied to evaluate the solubility of ketoprofen (KTP) in ethanol + water cosolvent mixtures at 298.15 K. Calculated values of molar volume and solubility parameter for KTP were used.A good predictive capacity of EHSA was found by using a regular polynomial model in order five to correlate the W interaction parameter and the solubility parameters of cosolvent mixtures (d mix ).Nevertheless, the deviations obtained in the estimated solubilities with respect to the experimental solubilities were on the same order like those obtained directly by means of an empiric regression of the logarithmic experimental solubilities as a function of d mix values.