Guilbert and Iscove demonstrated that precursor cells of erythrocytes and macrophages could be cultured in a totally defined serum free medium supplemented with albumin, transferrin, lecithin, and selenium. This medium is a modification of Dulbecco’s Modified Eagle’s Medium (DME) containing selenium, additional amino acids and vitamins, sodium pyruvate, HEPES buffer, and potassium nitrate instead of ferric nitrate.