Methanol uptake from methanol-water mixtures has been measured at ambient temperature in Nafion(R)117 membranes initially saturated with water. After equilibration for 18 h the membranes were dried at 70 degrees C in vacuum with a cold trap cooled with liquid nitrogen and the total amount of absorbent was determined from the weight loss. The methanol-water ratio was determined by H-1 NMR. A plot of the mole fraction of methanol in the membrane vs. the mole fraction in the water-methanol mixture was linear in the whole range from pure water to pure methanol. The slope indicated that Nafion(R) does not preferentially take up either water or methanol. The number of solvent molecules was found to be 23 per sulphonic group for both methanol and water.