Clinical hematologists are frequently faced with the intriguing problem of agnogenic myelo- dysplastic syndromes; these syndromes are peculiar in their failing or poor response to therapy and in that they frequently terminate in acute leukemia. An international symposium held in Innsbruck in 1978 was dedicated to clinical and pathophysiologic aspects of the preleukemic syndromes. This monograph consists of articles that correspond to the papers presented at the symposium and of the edited discussions. It was the aim of the symposium and of this monograph to outline comprehensively the pathophysiologic background of the preleukemic syndromes and to summarize the present information about their clinical management. The first part of the monograph covers that pathology of these disorders: Disturbed maturation and proliferation of the hemopoietic cells are the causes of cyto- penias, of structural and ultrastructural anomalies, and of enzymatic and functional defects. Further articles are concerned with the evaluation of these features and of chromosome anomalies as possible tools for the diagnostic and prognostic classification of myelodysplasias. Pathogenetic data and immunologic considerations form the rationale for therapeutic ap- proaches. F. Schmalzl K. -P. Hellriegel v Contents K. -P. Hellriegel and F. Schmalzl Preleukemia: Definition and Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H. Heirnpel Conventional Morphological Examination of Blood and Bone Marrow Cells in the Diagnosis of Preleukemic Syndromes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 C. Peschle Pure Red Cell Aplasia Type III: Progression to Acute Myeloid Leukemia and Absence of the IgG Inhibitor to Erythropoiesis . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Discussion . . . . . . . . . . . . . . . . . . '. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 . . . . I. Fohlmeister, H. E. Schaefer, K. -P. Hellriegel, and R.