Abstract A gas permeation technique has been employed to study the permeability, diffusivity and solubility of deuterium in the molybdenum alloy, TZM, a potential divertor material for future fusion machines. The measurements should provide design data useful for the calculation of the retention and recycling rates of hydrogen isotopes from divertors in ITER. Measurements were made on disc-shaped samples of 48 mm diameter and 0.1 mm thickness over the temperature range 515–742 K and for driving deuterium pressures in the range 5–50 kPa. It was found that the permeability varied in the Arrhenius manner and was very similar to that reported for pure molybdenum. However, the solubility was observed to be weakly exothermic, which has not been often observed for molybdenum. There was evidence of deuterium trapping affecting the observed diffusivity and solubility.