• Tumor necrosis factor–α and interleukin 1β have been shown to be medicators of meningeal inflammation in animal models of bacterial meningitis. The presence of both cytokines in cerebrospinal fluid (CSF) of patients with bacterial meningitis has been documented recently. In this study, we measured concentrations of interleukin 1β and tumor necrosis factor–α in CSF samples from 36 patients with nonbacterial (aseptic) meningitis, 13 of whom had culture-proved enteroviral meningitis, and from 14 control patients. None of the samples from patients with aseptic meningitis and from the controls had detectable tumor necrosis factor activity in CSF. Thirty-two (89%) of 36 patients with aseptic meningitis had detectable interleukin 1β in CSF (mean ± SEM, 48±11 pg/mL). These concentrations were significantly smaller than those previously reported in patients with bacterial meningitis (944 ± 128 pg/mL). Only 2 of the 14 control patients had detectable CSF interleukin 1 β concentrations of 21 and 42 pg/mL. A significant correlation was evident between interleukin-1β concentrations and white blood cell counts in the CSF of patients with aseptic meningitis. Our data suggest that the initial events of CSF inflammation in children with aseptic meningitis are different than those in patients with bacterial meningitis, and the participation of these two cytokines, especially tumor necrosis factor–α, is less critical to the process.