The interrelationship between the differentiation and expression of mRNA for transferrin in the HL-60 leukemia cell line was studied. Transferrin mRNA was expressed in HL-60 leukemia cells and the amount was 50% of that in the positive control cell line, HepG-2 cells. The expression of $T_f$ mRNA in HL-60 cells was not regulated by IL-1, IL-6 and $TNF-{alpha}$, respectively. The expression of $T_f$ mRNA in the differentiated cells into a granulocyte lineage by DMSO, or all-trans RA, was up-regulated (160-170% of control cells); whereas, the expression was not regulated in the differentiated cells into a macrophage lineage by PMA. These results suggest that the differentiation to a granulocyte lineage of HL-60 leukemia cells appear to be related with the upregulation of transferrin mRNA expression.