Anyone surveying physiological and pharmacological journals can readily see that the biological actions of calcium ion are of increasingly widespread current interest. The scope of investi gated actions and reactions in which a role for calcium ion is of some importance is so numerous as to convey the impression that calcium ion is everywhere and interacts with everything. This being so, the challenge in contemporary research is to focus on investigation of those actions of calcium ion which, in some manner, influence either significant physiological parameters or the manner in which pharmacological agents act. This multi-authored book originated from a more limited Symposium on Importance of Calcium as a Primary Locus of Drug Action co-chaired by myself and Dr. Frank R. Goodman at the April, 1977 FASEB meeting in Chicago. This Symposium was organized in response to a perceived need for increased communication among 2 workers in different areas of Ca +-related research. In the pro cess of selecting the maximum of six areas for presentation within the format provided, it soon became apparent that this would result in only a limited sampling of current research efforts. Expansion of the number of areas to fourteen within a book format appeared to be the most logical mechanism to provide a more coherent inter disciplinary approach to consideration of various aspects of the 2 roles of Ca + in drug action. This is not to imply that all rele 2 vant Ca +-related areas are surveyed within this volume.