Granulocyte-macrophage colony-stimulating factor (GM-CSF) is often used to treat leucopenia. Other haematopoietins may increase the number of circulating leucocytes with higher efficiency, but GM-CSF has additional effects that may be far more relevant than its haematopoietic activity. GM-CSF induces differentiation, proliferation and activation of macrophages and dendritic cells which are necessary for the subsequent T helper cell type 1 and cytotoxic T lymphocyte activation. GM-CSF haematopoietic and non-haematopoietic functions have pro-inflammatory and immune regulatory potential to treat a variety of autoimmune diseases and tumours. On the other hand, GM-CSF deficiency leads to various immune dysfunctions and the current utilization of GM-CSF as haematopoietic factor might be an accurate but very incomplete indication for a cytokine with vast clinical potential.