The transfer of benzodiazepine derivatives (diazepam, bromazepam, alprazolam, oxazepam, nitrazepam, clonazepam, chlordiazepoxide, flunitrazepam, midazolam and lorazepam) across the water [1,2-dichloroethane interface was studied using cyclic voltammetry. The partition coefficients of ionic species of benzodiazepines, log PXH+ were calculated from the transfer potentials measured at pH log PXH+ = log PXH+ - log P-X can be used in structure-activity correlations as it takes into account the effects of substituents on the main positions within the molecule.