This method is for determining rhenium in fresh and usedplatinum-containing catalysts in the range of 0.05 to 0.75%.Elements that produce colored ions in the dissolution orcolor-development step constitute a positive interference. Iron orcopper in moderate concentrations are reduced by stannous ion to acolorless state and, therefore, do not interfere. Molybdenum whichforms a red coloration with the stannous ion is the majorinterference. Directions for the separation of rhenium frommolybdenum are given. Analysis for molybdenum is by UOP Method833.