Because interleukin-1 beta (IL-1 beta) and cachectin (tumor necrosis factor) are thought to mediate the body's response to microbial invasion, we measured IL-1 beta and tumor necrosis factor concentrations in paired cerebrospinal fluid (CSF) samples (on admission to the hospital, CSF1; 18 to 30 hours later, CSF2) from 106 infants and children with bacterial meningitis. In CSF1, IL-1 beta was detected in 95% of samples; the mean (+/- 1 SD) concentration was 944 +/- 1293 pg/ml. Patients with CSF1 IL-1 beta concentrations greater than or equal to 500 pg/ml were more likely to have neurologic sequelae (p = 0.001). Tumor necrosis factor was present in 75% of CSF1 samples; the mean concentration was 787 +/- 3358 pg/ml. In CSF2 the mean IL-1 beta concentration was 135 +/- 343 pg/ml, and IL-1 beta concentrations correlated significantly with CSF2 leukocyte count, with glucose, lactate, protein, and tumor necrosis factor concentrations, and with neurologic sequelae. Tumor necrosis factor was detected in CSF2 specimens of 53 of 106 patients, with a mean concentration of 21 +/- 65 pg/ml. Of the 106 patients, 47 received dexamethasone therapy at the time of diagnosis. These patients had significantly lower concentrations of IL-1 beta and higher glucose and lower lactate concentrations in CSF2, and they had a significantly shorter duration of fever compared with the values in patients not treated with steroids (p less than or equal to 0.002). Our data suggest a possible role of IL-1 beta and tumor necrosis factor as mediators of meningeal inflammation in patients with bacterial meningitis, and might explain, in part, the beneficial effect of dexamethasone as adjunctive treatment in this disease.