The preparation of microelectrodes for use in various electrochemical mapping techniques (e.g., scanning electrochemical microscopy and photoelectrochemical microscopy) is described. A commercial optical fiber (3.7 mu m core diameter with 125 +/- 2 mu m and 245 +/- 15 mu m diam of cladding and coating, respectively) was stripped of its polymer coating at one end. The stripped core was then etched in different concentrations of hydrofluoric acid solution until a tip near 1 mu m in diameter was achieved. The resulting optical fiber was coated with gold by de-sputtering to produce a microelectrode less than 3 mu m in total diameter. The optical fiber microelectrode was then coated with an insulating varnish yielding a final tip size normally less than 5 mu m in diam. The final microelectrode was tested both for leaks in its polymer insulation and for electrical conductivity of the gold coating. The microelectrode has been used in several studies in our laboratories. Details of the preparation conditions are described here.