The electrochemical behavior and electrical conductivity of C-60 thin films were studied in acetonitrile containing M(bpy)(3)(2+) (M = Fe, Ni, Ru or Os; bpy = 2,2’-bipyridine). Cyclic voltammetry of C,, films showed stable reduction-reoxidation waves. In situ conductivity measurements indicated that an enhanced conductivity (on the order of 10(-2) S cm(-1)) appeared reversibly on electrochemical reduction accompanied by doping of M(bpy)(3)(2+) ions into the C-60 films. The electrochemical reduction also induced some structural change.