Optimizing platelet engraftment following hematopoietic stem cell transplantation is essential for minimizing transplant-related morbidity, particularly following umbilical cord blood transplantation (UCBT), where platelet engraftment frequently takes >60 days. One strategy for optimizing platelet engraftment following UCBT is to study or alter the genetic program of megakaryocyte/platelet (Mk/plt) progenitors. Retroviral vector gene transfer has previously proven useful for studying the biology of hematopoietic stem cells; however, procedures for transducing UCB cells of the Mk/plt lineage with retroviral vectors have not been described. We report here that Mk/plt progenitors generated from UCB progenitors can be efficiently transduced with retroviral vectors. Transduced Mk/plt cells were identified and quantitated by expression of a vector transgene encoding a truncated version of the human nerve growth factor receptor (NGFR). Vector-mediated NGFR expression could be readily detected in Mk/plt progenitors defined by immunophenotypic, morphologic, and functional criteria. In addition, NGFR expression persisted in mature anucleate platelets generated from the transduced Mk/plt progenitors. These methods may be useful for introducing genetic elements into Mk/plt progenitors to study various aspects of platelet development and biology and for marking ex vivo expanded Mk/plt progenitors to determine their contribution to engraftment.