A generator column method for measuring the octanol/water partition coefficient, K(o/w) and the aqueous solubility, C sup w sub s, is described. When water is pumped through a generator column packed with solid support coated with an organic stationary phase, an aqueous solution is generated that is in equilibrium with the stationary phase. The solute concentration in the eluted aqueous phase was measured either by high pressure liquid chromatography or by solvent extraction followed by gas chromatographic analysis. Aqueous solubilities and octanol/water partition coefficients of organic solutes, falling into 7 general chemical classes, have been systematically determined using the modified generator column method. From thermodynamics an equation is derived relating K(o/w) to the volume-fraction-based solute activity coefficient in water gamma sup w sub s, the latter being determinable from C sup w sub s. For each class of compounds, excellent linear correlations are found between log K(o/w) and log gamma sup w sub s with slopes close to the theoretical value of unity.