The in situ synthesis of micrometer and nanometer gold particles in polyaniline (PANI/Au composite) using chemical or electrochemical methods, has been compared. The direct chemical synthesis of PANI/Au is initiated via the spontaneous oxidation of aniline by AuCl4-. Gold colloid formation and subsequent reaction with PANI is monitored by in situ UV/vis spectroscopy. The emergent polymer nucleates on the gold as the PANI chain length increases, encapsulates the metal, and precipitates as its solubility limit is exceeded. Scanning electron microscopy images of these samples show relatively constant 1 mum diam gold particles. Electrochemical PANI/Au synthesis is initiated by AuCl4- reduction into an a priori electrochemically deposited PANI film. This method also produces a nearly uniform dispersion of Au particles but with significantly smaller 150-300 nm particles. The results indicate that electrochemical methods are more suitable for controlling particle dimensions. A minimal decrease in conductance is observed for the chemically formed PANI/Au when compared to PANI samples without the gold. A significant decrease in conductance is observed for the electrochemically formed composite. The large decrease in conductance is related to the decrease in proton doping and a greater number of oxidized units in the polymer upon electrochemical uptake and reduction of AuCl4-. (C) 2004 The Electrochemical Society.