The rapid growth of immunology has greatly increased our understanding of disease; this growth has also generated a subject which at times appears separated from some of the basic medical sciences. Recent studies in the areas of purine metabolism and of polymorphonuclear neutrophil phago cyte function have, however, linked immunology and clinical medicine with biochemistry. The precise defects of the inborn errors of metabolism have now provided good evidence for the importance of purine metabolism specifically the enzymes adenosine deaminase and nucleoside phosphorylase in lymphocyte function. In view of this and the steady advance of clinical and biochemical investigation of the polymorphonuclear neutrophil phago cyte, it appeared timely to review the inborn errors of immunity and phagocytosis at the fifteenth annual symposium of the Society for the Study of Inborn Errors of Metabolism at Elsinore, Denmark on September II-14th, I~77. The papers presented at that meeting form the basis of this volume which brings together contributions from immunologists, biochemists and clinicians. This interdisciplinary communication should be helpful to those concerned with immune function in their patients or in the laboratory. The book is divided into four sections, One: defects of cell-mediated immunity, Two: enzyme defects and immunodeficiency, Three: disorders of non-specific immunity and Four: screening for immunodeficiency. Section One contains two reviews, one on immunodeficiency from Robert Good's group in New York and another on the genetics of the immune system from Arne Svejgaard of Copenhagen.