The Second International Workshop on Human Leukocyte Differentia- tion Antigens was held in Boston, September 17-20, 1984. More than 350 people interested in leukocyte differentiation agreed to exchange reagents and participate in this joint venture. All in all, in excess of 400 antibodies directed against surface structures on T lymphocytes, B lymphocytes, and myeloid-hematopoietic stem cells were characterized. Because of the enormous quantity of serologic, biochemical, and functional data, Leuko- cyte Typing II has been divided into three volumes. These books represent the written results of workshop participants. They should be helpful to both researchers and clinicians involved in scientific endeavors dealing with these broad fields of immunobiology. To those who delve into the various sections of the volumes, it will become evident that the work speaks for itself. I am deeply indebted to the section editors, Barton F. Haynes, Volume 1, Human T Lymphocytes, Lee M. Nadler, Volume 2, Human B Lympho- cytes, and Irwin D. Bernstein, Volume 3, Human Myeloid and Hemato- poietic Cells for their major contributions in planning, executing, and summarizing the workshop, as well as council members John Hansen, Alain Bernard, Laurence Boumsell, Walter Knapp, Andrew McMichael, Cesar Milstein, and Stuart F. Schlossman. I would also like to thank the National Institutes of Health, World Health Organization, and Interna- tional Union of Immunological Societies for making this meeting possible.