Two series of alloys, (Zr36Ni64)(1-alpha)(Ti39Ni61)(alpha) and (Zr36Ni64)](alpha) (Hf36Ni64)alpha (0 less than or equal to alpha less than or equal to 1), were rapidly quenched by a single-roller, melt-spinning technique; amorphous alloy membranes 30-40 mum thick were obtained except for Ti39Ni61. X-ray diffraction showed that the amorphous structure was almost independent of Hf content but became denser with increasing Ti. Additionally, differential scanning calorimetry showed that thermal stability was improved by Hf, but not by Ti. Palladium-coated amorphous membranes were never broken during permeation testing in the range of 473 to 623 K. The permeation rate was rather stable at 573 K or less and approximately proportional to the square-root difference of hydrogen partial pressures across the membrane, suggesting that permeation was controlled by the diffusion process of hydrogen atoms in the membrane; it was also inferred that membranes had no defect that all other gases could pass through. Permeability was found to decrease with Ti or Hf due to increased activation energy for permeation. On the other hand, as-quenched Ti39Ni61 membranes were crystalline and too brittle to be used for hydrogen separation.