Granulocyte macrophage-colony stimulating factor (GM-CSF) is now best viewed as a major regulator governing the functions of granulocyte and macrophage lineage populations at all stages of maturation. There is recent evidence for a key role for GM-CSF in inflammatory and autoimmune diseases, therefore making it worthy of consideration for targetting. Such evidence includes disease exacerbation following its administration and amelioration of disease in animal models by GM-CSF gene targetting or by anti-GM-CSF antibody blockade. The interdependence of GM-CSF formation and that of the important proinflammatory cytokines, interleukin-1 and tumour necrosis factor-alpha (TNF-alpha), is discussed, as is the greater disease suppression found in arthritis models following GM-CSF depletion compared with that observed in the absence of TNF-alpha.