Hemopoietic precursor cloning in healthy donors and patients with lymphoproliferative disorders and its regulation in donors by two novel suppressive factors (BSF and ErSF) are investigated. It is shown that the count of erythroid precursors is increased in peripheral blood of patients with non-Hodgkin's lymphoma in contrast to the count of granulocyte-macrophage precursors. BSF inhibits entirely granulocyte-macrophage, macrophage and erythrocyte colony growth. In contrast, ErSF abrogates selectively erythroid precursor cell proliferation and differentiation. The role of the above factor in normal hemopoiesis inhibition mechanism during lymphoproliferative diseases are discussed.