Research on aplastic anaemia has until recently been limited to clinical description, morphology and epidemiology. New methods to culture haemopoietic cells, and advances in our knowledge of proliferation and differentiation in the haemopoietic cell system .opened a new area of scientific interest for this prototype of haemopoietic failure. In addition, bone marrow transplantation became not only a clinical method of treatment, but also a source of data useful for the discussion of pathophysiological models of aplastic anaemia. This situation prompted us to arrange an international con ference on aplastic anaemia, with particular emphasis on its patho physiology and the rationals of the current therapeutic approaches. This conference was held at Schloss Reisensburg from July 20-22, 1978 with the participation of both experimental and clinical scientists active in this field or in related areas of research. The proceedings of the symposion reflect the present knowledge as well as the many new questions which arose from the discussions. The editors are gratefully indebted to the participants of this meeting, to Gerlinde Trogele and all the co-workers of the Uni versity of Ulm engaged in preparation of this symposium and of this volume, and last not least to all sponsors who provided the financial basis for this scientific event.