A national inventory of the sources and emissions of the element molybdenum was conducted. The study indicated the preparation of an overall material flow chart depicting the quantities of molybdenum moving from sources of mining and importation through all processing and reprocessing steps to ultimate use and final disposition. All major sources of molybdenum-containing emissions were identified and their molybdenum emissions into the atmosphere estimated. A regional breakdown of these sources and their emissions was also provided. The physical and chemical nature of the molybdenum-containing emissions was delineated to the extent that information was available, and a methodology was recommended for updating the results of the study every two years. (Author)