Granulocyte-colony-stimulating factor (G-CSF) is a tissue-derived 25,000 Mr glycoprotein that stimulates neutrophilic granulocyte colony formation from murine bone marrow progenitor cells in vitro. It is also a potent inducer of terminal differentiation and suppressor of stem cell renewal in the murine myelomonocytic leukemic cell line WEHI-3B. Purified G-CSF was radioiodinated to high specific radioactivity with retention of full biological activity. Iodinated G-CSF bound specifically to WEHI-3B cells, J774 macrophage tumor cells, and normal murine bone marrow cells but not to a variety of other tumor cell lines or murine thymocytes. WEHI-3B cells showed a high affinity for 125I-labeled G-CSF (Kd = 90 pM) but displayed only a small number of specific receptors (300-700 per cell) at 37 degrees C. Other purified colony-stimulating factors showed no competition for binding to these receptors. WEHI-3B (D-), a subline of WEHI-3B that cannot be induced to differentiate by G-CSF, showed no specific binding of this factor, indicating that it is deficient in receptor presentation.