Molybdenum may exist in the atmosphere as the element, the oxide or as molybdates. Concentrations of molybdenum in ambient air range from below detectable amounts to maximum values in the order of 0.34 µg/m3 of air (1) . The satisfactory determination of molybdenum depends largely on the formation of an ex-tractable green complex by the reaction of molybdenum with 4-methyl-1, 2-dimercaptobenzene, also called toluene-3, 4-dithiol or dithiol (2). Iron interference can be prevented by reducing ferric iron to the ferrous state with potassium iodide and decolorizing the liberated iodine with sodium thiosulfate. The dithiol complex is extracted with methyl isobutyl ketone (MIBK). The MIBK extract is analyzed with an atomic absorption spectrophotometer using the operating conditions as recommended by the manufacturer (3).