Addition of sodium hydroxide to radioactive waste solutions produced a heterogeneous mixture of solids that exhibit different settling characteristics. Plutonium effectively coprecipitated with iron and uranium, and uranium with iron. Aluminum proved ineffective as a coprecipitating agent for either plutonium or uranium. Coprecipitation of uranium and plutonium occurs when the mole ratio of coprecipitating agent to actinide exceeds 1500. Addition of water to the alkaline slurries that simulate dilution during retrieval and pretreatment of high-level wastes results in dissolution of small amounts of uranium and plutonium in some slurries. The amount of uranium and plutonium dissolved did not saturate the solution in either actinide.