Small tension specimens of Sandvik 12R72HV and Inco IN-744X were injected with helium by means of α particle irradiation from a cyclotron to produce approximately uniform concentrations of from 1×10^-6 to 2.5×10^-5 atom fraction. The specimens subsequently were tension tested in vacuum between 500 and 800 C. Sandvik 12R72HV is significantly more resistant to helium embrittlement than Type 304 or 316 stainless steel. Helium in Inco IN-744X has little effect on the superplastic behavior of this alloy.