L1210 cells treated for 21 hours with S12363, a new vinca alkaloid derivative and the parent compounds (vinblastine, vincristine, vindesine) at equitoxic concentrations were found, by flow cytometry, to be equally accumulated in the G2 + M phase of the cell cycle. The chromatin structure of these cells was then analyzed in order to quantify with high precision the percentage of cells in mitosis. S12363 was found to accumulate, from the first hours of treatment (4-8 hours), and at lower concentrations, a higher percentage of cells in the M phase than the reference drugs. Taking into account previously published studies concerning the characteristics of vinblastine and vincristine uptake, our results are compatible with a facilitated uptake of S12363.