The work function of spin cast films of poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) was adjusted by electrochemical oxidation/reduction. The electrochemical equilibrium potential of these films was compared to the absolute value of the work function measured at dry films in ultra high vacuum by ultraviolet photoemission spectroscopy. A linear relationship between work function and equilibrium potential was found. It is shown that the redox state of the films is not changed by transferring the films into the dry state. The sodium content of the layers is strongly diminished after electrochemical treatment. (C) 2003 Elsevier B.V. All rights reserved.