The release behavior of uranium, plutonium, and neptunium from a defense waste reference glass was studied at 90 °C, alone and in the presence of ductile iron. Deionized water and simulated groundwaters for repositories in basalt and salt were used as test solutions. The initial surface area of glass to volume of solution was 10 m−1; the surface area of iron, where included, was equal to that of the glass sample. Solution samples were removed at regular intervals over 56 days, and actinide concentrations in unfiltered and 1.8-nm filtered (i.e., dissolved) portions were analyzed. The release behavior of uranium, plutonium, and neptunium did not show any consistent relationship to each other in any of the solutions, casting doubt on the use of uranium as a “master” indicator of actinide release. The presence of iron increased the initial rate of actinide release from the glass for all solutions, although the concentration of truly soluble actinides decreased. The difference is attributable to the formation of colloidal actinides. The actinide concentration in the filtered samples closely approaches the known solubility concentrations for hydrate oxides of these elements, suggesting a solubility-limiting control to the release of actinides from glass for time periods greater than several months.