Benzylaminopurine (6–BAP),as the derivative of adenine,is involved among cytokinins (CKs).CKs are phytohormones which participate in regulation of growth and development processes of plants. Methoxy and chlorine derivatives of 6-BAP show antitumor activity (inhibitors of cyclin–dependent kinases) and due to this effect may be considered as potential cytostatics.The aim of this contribution is the determination of protonation constants of 6–BAP and its derivatives by potentiometric method for the different experimental conditions,such as methanol content (2.5-20 v/v percentages),temperature (5-37C) and ionic strength (I=0.1-1M NaCl).To determine the thermodynamic parameters deltaH and deltaS the temperature dependence of pKa was employed.The effect of the position of methoxy and chlorine group (X is Cl or OCH3) in 2',3'and 4'on benzene ring of 6–BAP was studied,too.6–BAP and its derivatives were also studied using cyclic voltammetry and elimination voltammetry with linear scan (EVLS) and it was found,that addition of methanol in measured solution supported adsorption of above–mentioned ligands on mercury electrode.