We examined the effect of hemin, TGF-beta1 and cytosine arabinoside (Ara-C) on the levels of mRNAs for the erythroid-specific 5-aminolevulinate synthase (ALAS-E) and gamma-globin in various human myelogenous leukemia cell lines. Detailed analyses were also made using one of them, YN-1, which was isolated and established in culture from a patient with chronic myelogenous leukemia. Our results demonstrate that gamma-globin protein level and the percentage of benzidine-positive cells in the cell line increased markedly (10- to 30-fold) upon treatment with hemin, TGF-beta1, or Ara-C. In contrast, gamma-globin mRNA was already markedly expressed prior to treatment in 4 out of 9 cell lines examined, including YN-1, and the level increased only marginally after treatment with hemin. ALAS-E mRNA levels were increased in YN-1 cells after treatment with TGF-beta1 and Ara-C, while hemin treatment had little effect. These results indicate that heme supply is insufficient in YN-1 cells and suggest that hemin increases hemoglobin synthesis principally at the post-transcriptional level, whereas TGF-beta1 and Ara-C stimulate hemoglobin synthesis by activating efficient endogenous heme supply in the cells.