The influence of the nature of the organic solvent on the extraction of the thenoyltrifluoroacetonates of Np V, Co II and Ce III, the hydroxyquinolates of Np V and W VI, the acetylacetonates of Co II and Fe III, the 1-nitroso-2-naphtholate of Co II, and some other chelate compounds has been studied. As a rule, “co-ordination-unsaturated” chelates (co-ordination number of the central atom greater than twice its charge, bidentate reagent) are extracted better by ketones, esters, and, particularly, by alcohols; and, normally, are less well extracted by ethers and by hydrocarbons and their halogen-substituted derivatives. The extraction of “co-ordination-unsaturated” chelates can in some cases be favoured by the use of an excess of the reagent. “Coordination-saturated” chelate compounds (co-ordination number not greater than twice the charge, bidentate reagent) can be extracted by solvents of extremely diverse nature, including non-oxygen-containing solvents of relatively low polarity. Attention is drawn to the possibility of separating “co-ordination-saturated” and “co-ordination-unsaturated” chelate compounds.