A technique is presented for the direct measurement of octanol-water partition coefficients by HPLC. The method involves running solutes in octanol-saturated water as the mobile phase against water-saturated octanol entrained on an inert support. Log P correlates linearly with log tc for a number of standards. The measurable range in log P (so far) is -0.3 to +3.7. A critical review of chromatographic methods in Hansch analysis is given.