Platinum is determined in gold by activation analysis by means of199Au after separation of the matrix at the end of irradiation before the daughter nuclide forms. The method involves the radiochemical separation of gold by chloro-complex extraction with MIBK from 1N HCl, and energy-selective pulse counting of199Au at 158 keV. The irradiation problems are presented. The dependence of the extractability of the gold chloro-complexes on the acidity and the type of solvent are investigated. The procedure of analysis is described. The results obtained in determining 5–700 ppm Pt in Au, Pd and Rh are discussed.