The articles published in this volume are based on the papers delivered at a conference on the Role of Metal Ions in Biological Systems held November 20 and 21, 1972, at Argonne National Laboratory. The purpose of the conference was to present to an interdisciplinary audience of physical scientists some recent developments illustrating the chemical and environmental participation of the heavy metal ions in the biological system. The invited speakers at the conference are specialists in the fields they describe, and the articles presented here are at a level of interest to readers with backgrounds in physical sciences who are not necessarily doing research in the areas described. The articles are referenced through 1972, and in some cases early 1973, and thus should also be of value to research workers. It is hoped that the book will be of particular interest to chemists, biologists, workers in the fields of environmental science and public health, as well as graduate and senior undergraduate students in these disciplines. The conference was sponsored by the Central States Universities, Inc., a consortium of sixteen midwestern universities, the Center for Educational Affairs, Argonne National Laboratory, and the United States Atomic Energy Commission.