The partition of uranium (VI) between sulphuric acid solutions and solutions of tri-n-dodecylamine (TDA) in benzene has been investigated by varying the sulphuric acid concentration, aqueous uranium concentration, solvent concentration and temperature; the extraction of sulphuric acid by TDA in benzene has also been examined. Infra-red spectra have been obtained of the organic solutions involved. The mechanism of uranium extraction is discussed in the light of these results.