An accurate resistiometric technique for measuring fast diffusion of hydrogen in metals is described. The sample is in the form of a foil having uniform cross section and a length much greater than its width. Samples are electrolytically loaded with hydrogen to about 0.5 atomic percent. Initially the hydrogen is held at uniform concentration in essentially half the length of the foil by the effect of a dc electrotransport current of 2500 A/cm2in the other half. After this current is removed, the diffusion of hydrogen into the second half is monitored by its effect on the resistance of a small section of the foil. With this technique a single sample may be reused to make many measurements of D. The measurement ofDis absolute, and use of a sensitive differential ac measurement yields results for low hydrogen concentrations.