The solid-state electrochemical behavior of the luminescent conjugated polymer, poly[2-methoxy, 5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) and its blend with polyethylene oxide (PEO) was investigated by cyclic voltammetry and potential step experiments. It was found that the nature of the ions affects the ionic conductivity and the electrochemical odor behavior of the polymer(particularly on electrochemical n-doping). An electrochemical loop, which is similar to that observed in the electrochemical crystallization, was observed in the cyclic voltammetry of MEH-PPV/PEO(Li (+)) blend. The diffusion of the electrolyte ions is slow, but it was improved by the addition of PEG. The diffusion coefficient of the counterion in the bleed is up to 10(-8) cm(2) s(-1). These solid-state electrochemical results help to shed light on the mechanism of light-emitting electrochemical cells.