Research on the study of membrane toxicity has advanced a great deal in a relatively short period of time, prompting scientists to re-examine the problems associated with carriers, receptors and reactors to toxic substances. This book presents current research on the responses of membranes to toxic sub- stances both by direct observation of macromolecules reacting with these substances and by inference from data on the bio- chemical responses of cells and cell fractions. Two basic areas of membrane toxicity are analyzed by a large number and variety of scientists in this field. The first area is the effect of various toxic substances on membrane structure and function. The second area is where the membrane serves as the site of rate limiting step of the transport of various toxic substances. The aim of the book is to evaluate present concepts of membrane structure and function in relation to exposure to envir- onmental toxicants. The book is divided into five sessions: 1. Xenobiotics and Membrane Transport 2. Cellular Responses to Toxins 3. Effects of Membranes and Receptors 4. Modification of Membrane Function by Toxicological Agents 5. Toxic Chemicals as Molecular Probes of Membrane Structure and Function Each paper is generally concluded by an edited discussion which contains many useful and interesting additional insights in each subject area. v ACKNOWLEDGEMENT We gratefully acknowledge the support provided for this conference by the U. S. Energy Research and Development Administration, the Environmental Protection Agency and the University of Rochester.