In this study, the retention mechanisms on the Supelcosil LC-ABZ stationary phase were analyzed by linear solvation free-energy relationships (LSERs). In a first phase, a set of 60 compounds was selected by cluster analysis from a large set (253) compounds of known van der Waals volume (V-w), polarizability (pi*), H-bond donating acidity (alpha) and H-bond acceptor basicity (beta). The capacity factors log k' at 40% methanol and the log k(w), values were shown to be highly correlated with octanol/water partition coefficients (log P-oct) and to contain pratically the same structural information, as assessed by LSERs. Test sets of model compounds and dipeptides were used to validate the log k(w)/log P and log k'/log P relations. For anions and zwitterions, specific interactions with the stationary phase occur which produce systematic deviations in the log k/log P relations