In a previous study we reported that triethyllead (Et 3 Pb + ) inhibits cell proliferation of normal human lymphocytes. To further characterize this interaction, we studied herein the effects of Et 3 Pb + on the cell viability of normal and leukemic human lymphocytes and analysed the expression and dynamics of the monomer/polymer equilibrium of tubulin in these cells. Short- and long-term cell culture experiments demonstrated significantly different dose-dependent effects of Et 3 Pb + on cell viability of leukemic compared to normal lymphocytes. Indeed, in the presence of increasing concentrations of Et 3 Pb + (10 −12 –10 −5 M), primary cultures of chronic lymphocytes (CLL) and acute lumphoblastic (ALL) leukemic human lymphocytes were much more sensitive to Et 3 Pb + treatment when compared to normal peripheral blood lymphocytes (PBL). The ic 50 values were approximately 5 × 10 −6 M for PBL and 8 × 10 −10 M for both CLL and ALL respectively, when cells were preincubated for 3 h with this agent. These experiments revealed a 1000-fold higher responsiveness of leukemic cells to Et 3 Pb + treatment. Quantitative immunoblot analysis showed that leukemic cells express up to 4-fold higher total tubulin amounts. However, the proportion of polymerized tubulin in leukemic compared to normal lymphocytes increased only slightly (up to 1.4-fold). These findings reveal a significant decrease in the polymeric to total tubulin ratio in leukemic lymphocytes, indicating important modifications in tubulin dynamics and reorganization of the microtubular structures. Our results demonstrate that leukemic cells are much more sensitive than normal lymphocytes to Et 3 Pb + action. This effect may be due to the altered monomer/polymer dynamic equilibrium of tubulin shown in leukemic cells. It is, therefore, worthwhile exploring future applied uses of Et 3 Pb + as a potential suppressor of leukemic cell growth.