This study examined the effect of granulocyte-macrophage colony-stimulating factor (GM-CSF) on the ability of human monocytes and macrophages to kill the fungus Paracoccidioides brasiliensis. The researchers found that GM-CSF activated monocytes and macrophages in a concentration-dependent manner to kill P. brasiliensis. This fungicidal activity was associated with high levels of reactive oxygen species production by the activated cells. The killing effect was reduced by the addition of catalase, indicating a role for hydrogen peroxide. In contrast, inhibition of nitric oxide did not affect fungicidal activity, showing nitric oxide is not involved in killing P. brasiliensis. The results suggest GM-