The published data available on the insulin-like growth factor (IGF) family of peptides, its receptors and binding proteins in connection with normal and neoplastic hematopoietic processes are reviewed. It is found that nearly all the different hematopoietic cells, either normal or neoplastic, express IGF receptors. The IGFs are involved in normal erythropoiesis, granulopoiesis and lymphopoiesis. IGFs, especially IGF-1, are mitogenic for cell lines of myeloid and lymphoid leukemias and Burkitt's lymphoma. Differentiation of certain immature malignant cell lines is associated with a decrease in the number and affinity of IGF receptors. It might be concluded that the IGFs have an important role in the physiologic and neoplastic processes of the hematopoietic system, and the expanding knowledge of this issue will contribute to the understanding of proliferation and differentiation processes in specific hematologic disorders.