Isolation of resident macrophages from mouse tissues involves complex procedures for a small yield. This is inconvenient for many functional macrophage assays, which require large numbers of relatively homogeneous cells. An alternative method is the culture of bone marrow cells in vitro with appropriate growth factors, to allow the differentiation of precursor cells into large numbers of macrophages. This procedure is easy and inexpensive except for the use of M-CSF, the macrophage colony stimulating factor, and it is characterised by high yield and reproducibility. Once obtained, bone marrow-derived macrophages (BMMs) can be used for a considerable number of functional and structural assays and are commonly regarded as a model for the role of resident macrophages in the innate immune system.