Our purpose is to provide understanding for appropriate use of metals in a technical society. Knowledge of metal toxicity is needed for the preven tion, prediction, diagnosis, and therapy of adverse reactions from excess metals in mammals. Metal Toxicity in Mammals is presented in two volumes. Volume 1, Physiologic and Chemical Basis for Metal Toxic ity, provides the basis for understanding the toxic actions of metals recorded in Volume 2, Chemical Toxicity of Metals and Metalloids. The details and bases for many concepts summarized in Volume I are given, with appropriate references, in Volume 2. Thus, references for specific items in Volume 2 are not generally given in Volume 1. The authors reviewed the known toxicity of several heavy metals in anticipation of their use as multinutrient markers for NASA. As more and more metals were considered, the need for a complete review became obvious. This treatise supplants onerous searches of metal-toxicity litera ture up to 1975 and reviews the toxicity of all the metals of the periodic table on the basis of available relevant data. Books on pharmacological, nutritional, medical, veterinary, or industrial toxicity contain information about selected metals. More complete data about metals of public concern, such as mercury, lead, and cadmium, may be found in numerous books and reviews. The reader should refer to general texts and basic reference works, when specific references are not given, for general information.