The maintenance of normal primitive hemopoietic cell types in culture for long periods can be achieved either by culture of hemopoietic cells in association with bone marrow-derived stromal cells, as in long-term cultures, or by establishing factor-dependent primitive hemopoietic cell lines (FDCP-Mix cell lines). The long-term culture technique and a reproducible method for establishing FDCP-Mix cell lines will be described here (1 ,2 ).
