A methylisobutyl ketone/formamide two-phase organic solvent system was utilized for the separation of thallium(III) from the elements Ga, In, Fe(III), Sn(II) and Sn(IV). The procedure involves a semi-selective extraction of the elements from an aqueous 2MHBr solution with methylisobutyl ketone followed by the complete separation of thallium from the other elements enumerated by stripping the ketone phase with a 1.5MHBr-formamide solution. Thallium was determined at 3776 Å by flame emission spectrometry.