Results of 5 paired studies comparing the efficiency of different cytokine combinations for ex vivo expansion of megakaryocytic progenitors. In these experiments, CD34⁺ cells purified by negative depletion of lineage-positive cells were cultured in serum-free conditions. The basic cytokine combination included IL-6, IL-11, SCF, and MGDF. The addition of IL-3 and MIP-1α significantly increased the output of CFU-mega. When FL was included in the cytokine combination instead of (or together with) SCF, CFU-mega expansion was also significantly enhanced. Overall, MIP-1α, IL-3, IL-6, IL-11, FL, SCF, and MGDF was found to be the most effective cytokine combination. Results are reported as the average of the 3 clonogenic assays used. (a) P = .003 v IL-6, IL-11, SCF, MGDF; (b) P = .002 v IL-6, IL-11, SCF, MGDF; (c) P = .013 v IL-6, IL-11, FL, MGDF; (d) P = .003 v IL-3, IL-6, IL-11, FL, MGDF; (e) P = .001 v MIP, IL-3, IL-6, IL-11, FL, MGDF.