A method has been developed to estimate material properties uncertainties at radiation exposures beyond those of the present data base. The method can be used to assess the relative merit of materials testing in various neutron environments and to assess the relative merits of testing programs in various neutron sources. This approach has been applied to the materials testing program in FED/INTOR. The analysis indicated that testing austenitic alloy materials in FED/INTOR significantly reduce tensile property uncertainties after neutron exposures corresponding to a first wall loading of 3 MW.yr/m2. The uncertainty in swelling may not be reduced even if materials irradiation is extended to the present design goal for FED/INTOR of 6 MW.yr/m2.