A method for producing a collection of natural killer cells said method comprising i - culturing under static conditions cells of a sample comprising stem cells, progenitor cells or both, from human postembryonic tissue in a disposable bag for culturing mammalian cells, at a cell density of at least 0.5 x 10E 6 /ml for at least 7 days in a culture medium comprising human serum, a collection of cytokines and low molecular weight heparin, wherein said collection of cytokines comprises three or more of stem cell factor, flt-3Ligand (FLT-3L), thrombopoietin and interleukin-7 (IL-7) and three or more of granulocyte-macrophage-colony-stimulating factor (GM-CSF), granulocyte-colony-stimulating factor (G-CSF), interleukin-6 (IL-6), leukaemia-inhibitory factor and Macrophage-inflammatory protein-1alpha (MIP-I alpha) thereby obtaining a collection of cultured stem cells, progenitor cells or both, from human postembryonic tissue containing a plurality of progenitor cells committed to the NK cell lineage, and ii - culturing cells obtained in step (i) while the culture medium is mixed during culture, to enhance gas-exchange and to reduce the adherence of cells to a solid surface for at least 7 days at a cell density of at least 1 x 10E 6 /ml in a culture medium comprising human serum and a collection of cytokines, wherein said collection of cytokines comprises three or more of stem cell factor, interleukin-7 (IL-7), interleukin-15 and interleukin-2 and three or more of granulocyte-macrophage-colony-stimulating factor (GM-CSF), granulocyte-colony-stimulating factor (G-CSF), interleukin-6 (IL-6), leukaemia-inhibitory factor and Macrophage-inflammatory protein-1alpha (MIP-I alpha), thereby obtaining a collection of cultured cells containing a plurality of NK cells or NK progenitor cells or both. i - culturing under static conditions cells of a sample comprising stem cells, progenitor cells or both, from human postembryonic tissue in a disposable bag for culturing mammalian cells, at a cell density of at least 0.5 x 10E 6 /ml for at least 7 days in a culture medium comprising human serum, a collection of cytokines and low molecular weight heparin, wherein said collection of cytokines comprises three or more of stem cell factor, flt-3Ligand (FLT-3L), thrombopoietin and interleukin-7 (IL-7) and three or more of granulocyte-macrophage-colony-stimulating factor (GM-CSF), granulocyte-colony-stimulating factor (G-CSF), interleukin-6 (IL-6), leukaemia-inhibitory factor and Macrophage-inflammatory protein-1alpha (MIP-I alpha) thereby obtaining a collection of cultured stem cells, progenitor cells or both, from human postembryonic tissue containing a plurality of progenitor cells committed to the NK cell lineage, and ii - culturing cells obtained in step (i) while the culture medium is mixed during culture, to enhance gas-exchange and to reduce the adherence of cells to a solid surface for at least 7 days at a cell density of at least 1 x 10E 6 /ml in a culture medium comprising human serum and a collection of cytokines, wherein said collection of cytokines comprises three or more of stem cell factor, interleukin-7 (IL-7), interleukin-15 and interleukin-2 and three or more of granulocyte-macrophage-colony-stimulating factor (GM-CSF), granulocyte-colony-stimulating factor (G-CSF), interleukin-6 (IL-6), leukaemia-inhibitory factor and Macrophage-inflammatory protein-1alpha (MIP-I alpha), thereby obtaining a collection of cultured cells containing a plurality of NK cells or NK progenitor cells or both.