This study was aimed to investigate the effects of ouabain at low concentrations on growth regulation in various leukemia cell lines and to determine the therapeutic potential of ouabain in leukemia. By using MTT, flow cytometry (FCM), the changes in cell growth and cell cycle of leukemia cell lines were observed after treating with ouabain at low concentrations (<or=10 nmol/L). The expression of sodium pump alpha1 subunit was evaluated by Western blot. The results showed that in megakaryocytic leukemia M07e and Meg-01 cell lines, the low concentrations of ouabain (<or=10 nmol/L) inhibited the cell growth, blocked the cell cycle at G1 phase, and decreased the protein expression of sodium pump alpha1 subunit. The same concentrations of ouabain induced the proliferation of lymphocytic leukemia B95 and Jhhan cell lines, increased the percentage of cells at S phase and G2/M phase and up-regulated the expression of sodium pump alpha1 subunit. The basic expression of the sodium pump alpha1 subunit in M07e and Meg-01 was lower than that in B95 and Jhhan. It is concluded that the low concentrations of ouabain inhibit the cell growth of the megakaryocytic leukemia cell lines M07e and Meg-0, which may be related with the low expression of sodium pump alpha1 subunit of that cell lines and the negative regulation of the protein induced by ouabain.