Mineral metabolism may be altered in children with acute or chronic illnesses. The effects may be short term, such as hypomagnesemia associated with chemotherapy, or long-term, such as loss of bone mineral mass after steroid use. Understanding the causes, consequences, and potential therapies for mineral disorders is enhanced by understanding the absorption, body utilization, and turnover of these minerals. These assessments can now be done safely and readily using non-radioactive, stable isotopes which are available for calcium, zinc, magnesium, and iron. The methods for measurement of mineral absorption and kinetics (turnover) are well established, especially for calcium, and have been tested in every age group. Few studies, however, have been performed in children with acute or chronic illnesses such as cancer. Isotope dosing and infusion protocols are minimally invasive and protocols require small blood or urine volumes. Mineral absorption can be assessed without collecting fecal samples. Kinetics are assessed with blood and urine collections, usually over 5–10 days. Increased use of these techniques may be important in medical and nutritional assessment as well as in the management of pediatric oncology patients. Pediatr Blood Cancer © 2007 Wiley-Liss, Inc.