[en] The equilibrium hydrogen absorption isotherm using annealed, strain-free FeTi, exhibits only one plateau up to a composition of FeTiH_1.95. However, the desorption isotherm, determined immediately after the first hydriding step, exhibits the usual two plateaux. X-ray diffraction results of samples with compositions within the absorption plateau limits indicate the major phases present to be α and γ, although a small amount of β phase was always detected. Apparently the absorption isotherm represents the direct conversion of α → γ and β phase precipitation is almost completely suppressed. Thermodynamic quantities for this conversion are given. The results are attributed to the influence of lattice strain upon the behavior of the β1 and β2 phases. A practical consequence of the effect is the distortion of the pressure-composition isotherm in the β-γ region as a function of hydriding-dehydriding cycles. This is caused by an increase in H solubility of the β and γ phases and the widening of the phase composition limits as the strain increases with cycle number. However, after many hundreds of cycles there is no further significant increase in strain and the isotherm shape becomes essentially fixed and reproducible. The distortion is reversible by mild annealing