Methods for stabilizing blood samples, e.g., clinical blood samples, for storage or transportation before use. Exemplary applications include but are not limited to enrichment of leukocyte subtypes such as T-cells or neutrophils for cytokine and immuno-assays; isolation of progenitor cells from cord blood or peripheral blood for transplantation; isolation of fetal cells from the maternal blood for diagnosis; and sorting of circulating tumor cells for cancer detection and therapy.