AbstractExperimental conditions for the derivation of precise RM‐values are examined; the importance and the theoretical background of the extrapolation to modifyer‐free conditions as well as the generally proposed pK‐correction for RMare discussed. Compounds included in this study stem from the following four classes of drugs: antiarrhythmics, β‐blockers, phenothiazines and benzamides.RM‐values of these compounds (determined in acetonitrile/buffer) are compared with experimentally determined (log Pobs, log P*) as well as calculated log P values (∑f, C log P). Best interrelation is found with non‐pK corrected data derived in a buffer to modifyer mixture 50/50. Comparison of the calculative approaches indicates a slight superiority of