This volume gives an overview of the state of the art regarding cell-biological features of acute leukemias. Based on survey articles and results of clinical multicenter studies in children and adults with ALL or AML, it offers a detailed presentation concerning the significance of immunologic, cytogenetic and molecular-biologic analyses in the classification of acute leukemia and the identification of clinical risk groups. Current immunological and molecular-biological techniques for detecting minimal residual disease are described and their possibilities and limitations discussed. Further main topics include preclinical investigations and first clinical experience with interleukin 2-based immunotherapy in acute leukemia, biological features of new hematopoietic growth factors and recent advanced in the molecular understanding of the genetic defects in leukemic cells.