Electron beam melting has been used to obtain ultrapure refractory metals that are gaining importance in metal oxide semiconductor-very large scale integration (MOS-VLSI) processing technology, fusion reactor technology, or as superconducting materials. Although the technology of electron beam melting is well established in the field of production of very clean refractory metals, little is known about the limitations of the method because the impurity level of the final products is frequently below the detection power of common methods for trace analysis. Characterization of these materials can be accomplished primarily by in situ methods like neutron activation analysis and mass spectrometric methods [glow discharge mass spectrometry (GDMS), secondary ion mass spectrometry (SIMS)]. A suitable method for quantitative multielement ultratrace bulk analysis of molybdenum with SIMS has been developed. Detection limits of the analyzed elements from 10−7g/gdown to 10−12g/g have been found. Additional information about the distribution of the trace elements has been accumulated.