Three continuous human cell lines, designated KMOE, derived from a patient with acute erythremia (Di Guglielmo's disease) are reported. The cell lines are the cultures of (1) bone marrow cells, (2) peripheral blood cells, and (3) cells from a tumor developed into an athymic nude mouse after transplantation of the cultured bone marrow cells. Cells of all three lines show morphology of immature erythroblast and have i(17q) marker chromosome. They are negative for both Philadelphia chromosome and Epstein-Barr virus nuclear antigen. Although all KMOE cells in suspension culture are benzidine-negative, benzidine-positive cells are found within colonies formed in semi-solid culture media. The relative number of colonies with benzidine-positive cells is increased when sodium butyrate is added to the culture.