For 108 compounds of diverse chemical character (including drug molecules) isocratic reversed-phase liquid chromatographic retention parameters have been used in modifications of the Hildebrand-Scott equation to estimate compound aqueous solubility. The relationships found are valid for both liquids and crystalline solids, as well as for stronger ( pK a > 6.5) bases that are chromatographed in a partially ionized state. It is observed that there is a significant constant difference in behaviour between acid and alcohol molecules and neutral and base molecules. This difference can be empirically corrected for during solubility estimations. Comparison of the use of octan-l-ol/water distribution coefficients in these equations shows that the use of isocratic chromatograhic retention parameters lead to significantly better estimations of compound aqueous solubility.