Polyploidization is a part of the normal developmental process leading to platelet production during megakaryocyte (MK) differentiation. Ploidization is mainly involved in cell enlargement, but it is not clear whether gene expression is modified during MK ploidization. In this study, human MKs were grown from CD34⁺ cells in the presence of thrombopoietin and sorted according to their ploidy level. A pangenomic microarray technique was applied to compare gene expression in 2N-, 4N-, 8N-, and 16N-sorted MKs. Using hierarchical clustering, we demonstrated that 2N and 4N MKs or 8N and 16N MKs are 2 different close populations with 105 discriminating genes. In the second approach, we determined the profile of genes that were continuously down- and up-regulated during polyploidization. Among the 100 down-regulated genes, 24 corresponded to genes involved in DNA replication and repair. The great majority of up-regulated genes corresponded to genes directly involved in platelet functions, such as genes encoding specific platelet glycoproteins and α-granule proteins, actin and microtubule cytoskeleton, factors involved in signaling, and transport proteins. Together, these results suggest that MK polyploidization per se does not regulate gene expression but is intrinsically included in the differentiation process.