Inhibition of extracellular signal-regulated kinase (ERK) 1/2, p38 decreases lipopolysaccharide (LPS)-induced production of IL-1β, IL-6, TNF-α and nitric oxide (NO) in granulocyte macrophage-colony stimulating factor (GM-CSF)-treated microglia. Microglia were pretreated with U0126, SB 203580, or both, for 1 h and stimulated with GM-CSF (20 ng/ml) or left untreated for 48 h. Then the cells were harvested, washed twice, and seeded at a density of 1 × 105 cells/well in 24-well plates. Cells were further stimulated with LPS (1 μg/ml) for 48 h. Concentrations of IL-1β, IL-6, TNF-α and NO were determined by ELISA and the Griess method respectively. Data indicate mean ± SD. Data are representative of two independent experiments. ***P < 0.001 (between GM-CSF-primed and -unprimed), †††P < 0.001 (between GM-CSF-primed and SB 203580-pretreated), ‡‡‡P < 0.001 (between GM-CSF-primed and U0126-pretreated), §§§P < 0.001 (between GM-CSF-primed and SB 203580 + U0126-pretreated).