Bone marrow transplantation, the goal which integrates hemato logists, immunologists, geneticists, oncologists and specialists of several other fields, has overcome its state of stagnation in recent years. Clinically as well as experimentally new approaches to old problems and new conclusions from recent findings proliferate: bone marrow transplantation in leukemic remission, bone marrow growth in cell culture, bone marrow manipulation with antisera, bone marrow differentiation in histoincompatible hosts, immuno suppression with partial body irradiation to cite just a few. These and other new developments were discussed by experts from 12 countries in and outside the European Community during an international seminar held on March 8-10, 1979 by the "Institut fur Hamatologie, GSF", under the auspices of the European Communities. The editors thank both the contributors to this symposium, who made it a successful meeting and submitted their manuscripts punctually, and the publishers, who have provided a volume of high quality in good time. They are also grateful for the valuable cooperation from numerous colleagues at the Institut fur Hamato logie.