Formic acid has been proposed as a possible fuel for miniature fuel cells, because formic acid is expected to show low crossover and easywater management. In this paper, the permeation of formic acid through Nafion((R)) membranes is investigated at room temperature. It is found that the permeation of formic acid through Nafion((R)) 112 and 117 is much lower than that of methanol. For example, at a 1 M concentration, the steady state flux of formic acid through Nafion((R)) 117 is only 2.03 +/- 0.07 x 10(-8) mol/cm(2) s. By comparison, previous workers have observed a methanol flux of 3 to 6 x 10(-6) mol/cm(2) s through Nafion((R)) 117 under similar conditions. The flux through Nafion((R)) 117 increases with increasing formic acid concentration, reaching a maximum of 1.86 +/- 0.11 x 10(-7) mol/cm(2) s at a formic acid concentration of 10 M. The flux of formic acid is about a factor of two higher through Nafion((R)) 112 than through Nafion((R)) 117 but still low. These results show that the permeation of formic acid through Nafion((R)) is much slower than the permeation of methanol through the same membrane. Consequently, formic acid is an attractive alternative fuel for small polymer electrolyte membrane (PEM) fuel cells. (C) 2003 Elsevier Science B.V. All rights reserved.