A volumetric procedure is described for determining small amo-unts of iridium (from 2 to 20 mgm.). A solution of the metal is heate-d to dense fumes with sulphuric acid, codled, dilr,t"d rvith water, and then oxidized lvith an excess of cerium (IV)'sulphate solution. The resultant solution is titrated rvith a standard 0.01 N iron (Ii) sulphate solution, the course of the titration being followed potentiometrically. in solutions containing other platinum metals it has been iound possible to determine iridium directlf in some cases by this.procedure; in other cases it w'as found necessary to remove osmium as the volatile tetroxide prior to oxidizing with cerium (I\i) sulphate. The method.is probably less accurale than exisLinlg gravimetric prtcedrires. but offer' considerable advanrage in simplicity.