Leukotriene B 4 (LTB 4) is an important proinflammatory lipid mediator generated by neutrophils upon activation. GM-CSF stimulation is known to enhance agonist-mediated LTB 4 production of neutrophils within minutes, a process called “priming”. In this study, we demonstrate that GM-CSF also limits the production of LTB 4 by neutrophils via a transcriptional mechanism at later time points. We identified hemopoietic-specific Ras homologous (RhoH)/translocation three four (TTF), which was induced following GM-CSF stimulation in neutrophils, as a key regulator in this process. Neutrophils derived from RhoH/TTF-deficient (Rhoh−/−) mice demonstrated increased LTB 4 production upon activation compared with normal mouse neutrophils. Moreover, neutrophils from cystic fibrosis patients expressed enhanced levels of RhoH/TTF and generated less LTB 4 upon activation compared with normal human neutrophils. Taken together, these data suggest that RhoH/TTF represents an inducible feedback inhibitor in neutrophils that is involved in the limitation of innate immune responses.