The combination of a collision/reaction cell (C/RC) with a quadrupole/single focusing magnetic sector inductively coupled plasma mass spectrometer has been regarded as promising in reducing interfering ions while maintaining ample sensitivity for ultra-trace measurements of analytes, even in complicated matrices. Commonly used reagent gases, such as H 2 , He and NH 3 , have been successful in the determinations of a number of elements using isotope dilution mass spectrometry (IDMS). This review focuses primarily on recent applications of C/RC technology in IDMS. We also cover other issues, including equations for IDMS, currently available instrumentation and potential areas for future development.