An exploratory study of the effects of Cl- on direct methanol fuel cell (DMFC) performance is reported. Trace amounts of Cl- in methanol solution considerably degraded cell performance, with the extent depending on Cl- concentration. Recovery of cell performance was not observed after flushing with hot water for 20 h. The results of methanol-stripping voltammetry showed that the initial and peak potential for methanol oxidation shifted to higher values. Impedance measurements also suggested that the charge-transfer resistance for methanol oxidation became higher after Cl- poisoning. (C) 2005 The Electrochemical Society.