A method is provided for producing a population of post-mitotic cells of the neutrophil lineage, which method comprises the ex vivo steps of: (a) providing a population of cells comprising neutrophil progenitor cells; and (b) culturing the population of cells in an animal cell culture medium comprising (i) one or more early acting cytokines and (ii) one or more cytokines that differentiate said progenitor cells into a neutrophil specific lineage, under conditions of low oxidative stress, the culture medium being agitated when the cells are at a cell density at which oxygen transfer via the surface of the culture medium is insufficient for growth of the progenitor cells and the progeny thereof under static conditions, to produce a population of post-mitotic cells of the neutrophil lineage. The resulting population of cells can be used to increase the number of neutrophils in a patient.