Cytokines are cellular growth factors which also provide communication between cells and their milieu. This clearly is an exciting area in modern medicine that will have significant impact on various facets of transfusion. Erythropoietin therapy stimulates red cell production while thrombopoietin seems to positively affect megakaryopoiesis and can be an added armamentarium for the thrombocytopenic patient. Using haematnopoietic growth factors, stem cells could be mobilized early to the peripheral blood for collection and subsequent transplantation into haemato-oncology patients instead of bone marrow transplantation. Using a cocktail of cytokines in cell culture, stem cells could be expanded and selected for therapy. Cytokines and growth factors can even be modified, which may lead to successful gene therapy in malignancies, including solid tumour vaccines. However, the presence of cytokines in certain blood products could have biological effects following transfusion, although its clinical relevance needs to be ascertained. There is much potential for the use of cytokines in the treatment of infections. Early diagnostic methods are now available to monitor their levels and relevance. It is likely that cytokines will increasingly play a role in therapy and could develop our fundamental knowledge about the development of T-cells. An ethical dilemma remains, however, regarding the use of cytokines in healthy donors for harvesting suitable specific cells. Longer clinical observation will be necessary to gather the necessary information. Cytokines and growth factors in blood transfusion was the theme of the 21st International Symposium in Blood Transfusion, where twenty clinicians and scientists, experts in their own fields, were invited to update the above information. Their findings are presented in four sections in this volume: Fundamental aspects - cytokines in development of T-cells, growth factors in haematopoiesis, growth factor receptors and signal transduction, cytokine response in platelet and whole blood transfusions. Function, production and diagnosis &endash; laboratory diagnostics of cytokines and growth factors, cytokines in blood components, cytokines and growth factors in cell expansions, cytokines for genetic modification towards gene therapy, progenitor cells from healthy donors. Application in clinical medicine &endash; clinical relevance of cytokines in transfusion products, cytokines and growth factors in solid tumours, gene therapy in malignancies, vaccine strategies inducing T-cell immunity against tumours, cytokines in the treatment of infections, thrombopoietin and megakaryopoiesis. Future potential use in transfusion medicine &endash; erythropoietin, immunotherapy, ethical aspects of the use of cytokines and growth factors in donors, potential of cytokines and growth factors in transfusion medicine.