Friend leukemia cells (FLC) induced to erythroid differentiation by 5 mM hexamethylenebisacetamide (HMBA) are suitable for studies focused on the expression of different genes involved in the same differentiative program. In our studies FL cells have been cultured in alpha-medium (Gibco), 10% fetal calf serum (FCS, Flow Laboratories). Erythroid differentiation has been analysed by benzidine staining of the cells and globin synthesis by pulse-labelling the cells with 3H-leucine (New England Nuclear) and electrophoresis of newly-synthesized proteins on polyacrylamide gels. Hemoglobin production was determined by cellulose acetate gel electrophoresis. Our results demonstrate that heme synthesis is suppressed by the iron-chelator desferrioxamine. In addition "commitment" to erythroid differentiation and transcription and translation of globin mRNAs occur in HMBA-treated FLC in the absence of heme accumulation.