We describe the results of a novel adaptation of the volumetric technique to measurement of the pressure concentration isotherms for thin films of the palladium‐hydrogen system. The isotherm shapes are comparable to bulk being steep in the alpha and beta phases and flat in the mixed phase region. However, it is noted that the concentration onset of the beta phase is smaller than bulk and drops markedly for thicknesses less than 670 A˚. Comparison is made with quartz crystal microbalance results. We find a thickness dependence to the number of absorption‐desorption cycles required to obtain reproducible isotherms.