As one of many tasks of an analytical chemistry program sponsored by the office of Pesticides and Toxic Substances, Field Studies Branch, U.S. Environmental Protection Agency (EPA) (EPA Prime Contract No. 68-02-3938), Midwest Research Institute (MRI) prepared these summaries of the mammalian toxicology of 52 individual elements (metals and metalloids) and the lanthanides (rare earth elements). MRI is assisting the EPA in developing protocols for the monitoring of selected metals and organic compounds in the blood of the general U.S. population. The monitoring will enable evaluation of changes in the blood levels over time and any trends associated with instituted control measures. This review will help EPA select the metals to be included in the monitoring effort based on toxicity, relative exposure, and the ability of blood measurements to reflect exposure.