The Wharton's jelly of the umbilical cord is rich in mesenchymal stem cells (UC-MSCs) that fulfill the criteria for MSCs. Here we describe a novel, simple method of obtaining and cryopreserving UC-MSCs by extracting the Wharton's jelly from a small piece of cord, followed by mincing the tissue and cryopreserving it in autologous cord plasma to prevent exposure to allogeneic or animal serum. This direct freezing of cord microparticles without previous culture expansion allows the processing and freezing of umbilical cord blood (UCB) and UC-MSCs from the same individual on the same day on arrival in the laboratory. UC-MSCs produce significant concentrations of hematopoietic growth factors in culture and augment hematopoietic colony formation when co-cultured with UCB mononuclear cells. Mice undergoing transplantation with limited numbers of human UCB cells or CD34(+) selected cells demonstrated augmented engraftment when UC-MSCs were co-transplanted. We also explored whether UC-MSCs could be further manipulated by transfection with plasmid-based vectors. Electroporation was used to introduce cDNA and mRNA constructs for GFP into the UC-MSCs. Transfection efficiency was 31% for cDNA and 90% for mRNA. These data show that UC-MSCs represent a reliable, easily accessible, noncontroversial source of MSCs. They can be prepared and cryopreserved under good manufacturing practices (GMP) conditions and are able to enhance human hematopoietic engraftment in SCID mice. Considering their cytokine production and their ability to be easily transfected with plasmid-based vectors, these cells should have broad applicability in human cell-based therapies.