Inductively coupled plasma mass spectrometry (ICP-MS) has been applied with increasing frequency in the study of human nutrition and heavy metal toxicity. ICP-MS provides reliable isotope ratio determinations and superior metal concentration sensitivity. When combined with compound separation technology as part of the sample introduction phase, ICP-MS extends the tools available for studies of human metabolism and heavy metal poisoning. The basis for ICP-MS in these fields is reviewed, and examples are presented for zinc nutrition and lead toxicity to demonstrate the advances achieved in ICP-MS. The prospect for kinetic models with ICP-MS data is explored.