[en] Tungsten filaments derive their unique high temperature creep resistance and strength from the addition of small amounts of K, l, and Si, which are added to WO₃ prior to its reduction with hydrogen. The Direct Imaging Secondary Ion Mass Spectrometer was used in the identification of potassium-filled voids in annealed tungsten. The capabilities of the instrument are further explored. Preparation of specimens that include annealed rods and 65 μm dia lamp filaments is described. Ion images show the distribution of the dopant elements at various annealing stages. Ion sputtering of K-filled voids yields secondary ion bursts that are used to measure their number density in annealed tungsten. The redeposition of tungsten in burned regenerative cycle lamps was studied using the instrument. (U.S.)