A room-temperature molten salt, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) with adequate purity was obtained simply by the reaction of 1-ethyl-3-methylimidazolium chloride and tetrafluoroboric acid. Silver tetrafluoroborate dissolves up to similar to0.2 mol dm(-3) in EMIBF4 at room temperature. Electrochemical deposition and dissolution of silver on a platinum electrode were found possible in EMIBF4 containing AgBF4. The reduction of monovalent silver species is electrochemically irreversible, the rate constant being estimated to be 1 X 10(-5) cm s(-1). The diffusion coefficient of Ag(I) is calculated to be 6 x 10(-7) cm(2) s(-1), suggesting that Ag(I) exists as a substantially bare cation (Ag+) in EMIBF4. (C) 2001 The Electrochemical Society. All rights reserved.