Partition properties, that is partition coefficients and enthalpies (delta Hp degree) and entropies (delta Sp degree) of partition, have been measured for 50 benzoic acids in the 1-octanol/water system, and their role in QSAR (quantitative structure-activity relationship) analysis examined. The novel hydrophobic parameters have been introduced as a result of the separation of the Gibbs free energy term into the corresponding enthalpy and entropy terms. Application of these novel parameters to some available biological activity data supported the usefulness of these parameters in QSAR analysis. Relative contributions of the enthalpy and entropy terms are also discussed.