Research work at A.E.R.E. is reviewed under the following headings: (i) Chemistry of Diluent Degradation; (ii) Methods for the Cleanup and Disposal of Degraded TBP-Hydrocarbon Solvents; and (iii) Treatments to Improve Kerosene as a Diluent and Comparisons of Alternative Diluents. The performance of diluents has been rationalized on the basis of their composition (determined by vapor-phase chromatography), reaction with nitrous acid, and the subsequent reactions of nitroparaffins with acids and alkalies. There is evidence that the species responsible for the retention of zirconium in degraded solvents are hydroxamic acids (Alkyl-CONHOH) and their formation from nitroparaffins is outlined. Nitroparaffins readily form salts with alkanolamines and a complete removal of complexing agents from degraded solvent has been possible on this basis by extraction with certain alkanolamines which are insoluble in TBP-kerosene. Alkaline hydrogen peroxide shows promise for the removal of firmly bound uranium in solvents. Chemical methods are outlined for the separation of TBP from its diluents as a preliminary step towards disposal or recovery of badly degraded solvent. Pretreatment processes for improving kerosene, and a new class of stable diluents, the conjunct polymers of simple olefins, are described.