IL-16 is an immunomodulatory cytokine that is characterized by chemotactic activity and stimulation of proinflammatory cytokine expression in monocytic cells. We studied IL-16 using ELISA in children with meningitis. When meningeal symptoms existed, IL-16 levels were high in the cerebrospinal fluid (CSF) of both bacterial (939 ± 877 ng/l, n = 20) and aseptic (341 ± 371 ng/l, n = 23) meningitis. The values in the CSF were significantly higher than those in non-meningitis controls (29 ± 8 ng/l, n = 22, P < 0·0001). After meningeal symptoms disappeared, IL-16 levels in bacterial (191 ± 149 ng/l, n = 10, P = 0·0042) and aseptic (159 ± 188 ng/l, n = 13, P = 0·0118) meningitis were lower than those during the symptomatic stage. IL-16 levels were the highest before day 5 of the illness and then gradually fell. Significant correlations were found between IL-16 levels and both G-CSF levels (r = 0·783, n = 11, p = 0·0029) and IL-6 levels (r = 0·818, n = 12, P = 0·0005) in the CSF of bacterial and aseptic meningitis. IL-16 levels in all CSF samples from non-meningitis controls were lower than those in serum. In contrast, IL-16 levels in the CSF in six of 16 samples from bacterial meningitis and two of 18 samples from aseptic meningitis were higher than those in serum. Serum levels of IL-16 did not fluctuate throughout the course of meningitis. These data indicate that IL-16 levels rise transiently in CSF at the initial stage of meningitis. We speculate that IL-16 may promote inflammatory responses during meningitis in concert with other proinflammatory cytokines.