Charge control agents for liquid development were evaluated by electrochemical measurements, cyclic voltammetry and pulse voltammetry. Characteristics of charging were easily founded at high speed by these electrochemical methods. The NH standard potential of the charge control agent (versus NHE) was obtained and converted into an ionization potential. The control of charging in developing materials was adequately explained by the redox potential of the charge control agent. The present article reports that the best combination can be predicted by measuring redox potentials before formulating the toner.