We report an adaptation to cultures of chicken bone marrow cells of the Dexter culture technique for obtaining long-term hemopoiesis in vitro. Cells were seeded in DMEM supplemented with fetal calf serum (20%) and hydrocortisone (10(-6) M) with or without chicken serum (1%). Cultures were incubated at 37 degrees C and fed every 2 weeks. An adherent cell layer composed of macrophages, fibroblasts, and adipocytes became established, over which hemopoietic cells formed foci and were released into the supernatant. Granulocytes and monocytes-macrophages differentiated in a constant proportion until Week 6, whereafter differentiation became progressively restricted to the monocytic lineage. As demonstrated by the generation of colony-forming cells, hemopoiesis was maintained for either 12 or 28 weeks.