Concentrations of interleukin 1-beta and tumor necrosis factor in cerebrospinal fluid (CSF) of 42 neonates with Gram-negative enteric bacillary meningitis were determined and correlated with outcome and other CSF indices. At the time of diagnosis interleukin 1-beta was detected in CSF of 40 infants and peak concentrations correlated significantly with outcome from disease. Days of interleukin 1-beta concentrations of greater than 200 pg/ml or greater than or equal to 20 pg/ml were significantly correlated with days that CSF cultures were positive and that K1 antigen and endotoxin were detected in CSF. Tumor necrosis factor activity was detected in CSF of 25 of 27 infants; there was no correlation between outcome and CSF tumor necrosis factor concentrations. The results provide a possible rationale for therapeutic intervention to improve outcome.