Proliferation and differentiation of purified CD34⁺ cells cultured in the presence of MIP-1α, IL-3, IL-6, IL-11, FL, SCF, and MGDF was evaluated by means of two-color staining with PE-labeled anti-CD34 (vertical axis) and FITC-labeled anti-CD61 (horizontal axis) antibodies. The first panel represents a control obtained with irrelevant antibodies, and the percentage of positive cells per each quadrant is indicated. The flow cytometry analysis shows the presence of a small subset of CD34⁺ cells that are also CD61⁺ among cells seeded on day 0. The number of CD34⁺/CD61⁺ cells increased on day 5, and expansion peaked on day 7. Cells expressing the CD34⁺ phenotype were still present during the first week of culture. Conversely, on day 12 most of the CD34⁺ cells were already differentiated, and 39% of the cells acquired the CD34⁻/CD61⁺ phenotype. The results of one representative experiment of five are shown.