Pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF) administered after acute myeloid leukemia (AML) chemotherapy (CT) failed to shorten the time of transfusion-dependent thrombocytopenia in a previous study. In this multicenter, randomized, placebo-controlled, double-blind study we determined the effect of administration of PEG-rHuMGDF prior to CT and of administration prior, concurrent, and 1 day post CT on platelet recovery and transfusion requirements in patients receiving consolidation CT for de novo AML. Patients were randomized to receive either 30 microk/kg PEG-rHuMGDF as a single dose on day -6 ( n=37), placebo as a single dose on day -6 ( n=9), 30 microk/kg PEG-rHuMGDF administered on day -6 followed by 10 microg/kg on days -5 to day 6 (through CT and including the day after CT, n=35), or placebo administered on day -6 to day 6 ( n=9). The median times to transfusion-independent platelet recovery to >20x10(9)/l were 24.5 and 24.0 days in the PEG-rHuMGDF day -6 group and PEG-rHuMGDF day -6 to 6, respectively, compared to 21.0 days in the placebo group. There were no significant differences in the number of days of platelet transfusions between either PEG-rHuMGDF schedule or placebo. The PEG-rHuMGDF day -6 to 6 group had a delayed absolute neutrophil count (ANC) recovery compared to either placebo or PEG-rHuMGDF day -6 treated patients. Thus, alteration of the scheduling of PEG-rHuMGDF in terms of earlier dosing before and during chemotherapy did not improve platelet recovery but rather delayed hematopoietic reconstitution. Although unexpected, these observations may be of major relevance for the design of future clinical trials with recombinant thrombopoietins.