X-ray diffraction and Auger-electron spectroscopy depth profiling experiments clearly show that an interlayer reaction in a Ni/V bilayer forming Ni₃V and Ni₂V takes place at a temperature around 823 K when it is annealed in vacuum. However, this reaction temperature is reduced down to around 773 K when it is annealed in 0.5 MPa H₂. A similar effect has also been observed for a Ni/Nb bilayer previously. These hydrogen-enhanced reactions in the two systems are interpreted to be due to formation of abundant vacancy-hydrogen complexes in the V and Nb layers, which efficiently assist the interdiffusion of the constituent atoms across the interfaces in the two bilayers.