Changes in cell composition and viability as well as the content and functional activity of hemopoietic progenitor cells were analyzed during long-term (up to 1 month at 4°C) storage of human umbilical cord blood cells. No significant quantitative changes in erythrocytes were found during this period. The total content and viability of leukocytes changed, which resulted in the prevalence of mononuclear cells (lymphocytes and monocytes). Analysis of functional activity of hemopoietic stem cells in semisolid culture revealed a decrease in the relative content of CFU during the first week of storage [corrected] and inability of cells to colony formation after 2 weeks.