The logarithm of the retention time (log RT) of organic chemicals on a permanently bonded (C-18) reverse-phase high-pressure liquid chromatography system is shown to be linearly related to the logarithm of the n-octanol/water partition coefficient (log P). A rapid, inexpensive technique based on reverse-phase high-pressure liquid chromatography has been developed to estimate the n-octanol/water partition coefficient of organic chemicals. The system consists of a preparative Micro-Pak(R) C-10 reverse-phase column eluted with a 15% water/85% methanol solvent flowing at 2 ml/min at room temperature. A linear calibration of the logarithm of retention time with the logarithm of the partition coefficient (log P) is attained by using a mixture of benzene, bromobenzene, biphenyl, bibenzyl, p,p'DDE, and 2,4,5,2',5'-pentachlorobiphenyl as reference standards of known log P. Using a calibration mixture, the log P of other organic chemicals were estimated with a mean accuracy of 22.8% of the log P values reported in the literature. The technique permits estimation of log P in a maximum of 25 min and does not require a knowledge of the structure of the chemical for the estimate.