Electrochemical reduction of graphite and fullerenes has been carried out in solid state cells operating with solid polymer electrolytes based on poly(ethyleneoxide), (PEG), complexed with lithium perchlorate. Low speed cyclic voltammetry, galvanostatic reduction and oxidation experiments give evidence for different successive redox states which appear during the cycling of both carbon materials. Preliminary electron diffraction studies have been performed on selected intercalated fullerenes.