The effect of 1-hydroxyethane-1,1-diphosphonic acid (HEDPA) on the sorption of Np(V) and Pu(V) to synthetic boehmite (-AlOOH) was examined as a function of time and pH (between 4 to 11). The sorption of both elements in boehmite suspensions (1M NaCl, 600mgL-1 boehmite) increased with increasing pH. The sorption edges for neptunium and plutonium occurred at approximately pH 8.0 and 6.6, respectively. After steady state partitioning was reached, HEDPA was added to the neptunium-boehmite and plutonium-boehmite suspensions. Neptunium and plutonium partitioning appears to be primarily affected by the formation of soluble Np:HEDPA and Pu:HEDPA complexes, the dissolution of boehmite promoted by HEDPA, and the precipitation of Np:HEDPA and Pu:HEDPA colloids. The results are discussed in terms of applicability of HEDPA-promoted dissolution as a waste reduction method in the treatment of sludge phases contained within high-level nuclear waste storage tanks.