Lipopolysaccharide (LPS)-induced inflammatory factors production by the cerebral cortical glial cells in two sides of the murine brain are different. To determine if microglial cells, a subset of glial cells, are involved in asymmetric production, interleukin-6 (IL-6), interleukin-1β (IL-1β) and nitric oxide (NO) responses to LPS by microglial cells in the right and left cerebral cortices were examined. Primary microglial cells were isolated from BALB/C neonatal mice, treated with LPS (10 µg ml(-1) ) for 24 h and examined for IL-6, IL-1β and NO production. At untreated state, the levels of IL-6, IL-1β and NO showed no statistical difference between left and right. However, after LPS treatment, the levels of IL-6, IL-1β and NO for the right microglial cells was statistically significant higher than the left (P < 0·05). Our results denote that enhanced production of IL-6, IL-1β and NO after LPS treatment in microglia is directly proportional to their basal-state levels, and right cortical microglia produce higher levels of IL-6, IL-1β and NO than left cortical microglia.