The level of granulocyte-macrophage colony-stimulating factor (GM-CSF) in the cerebrospinal fluid from 14 infants and children with meningitis and 6 patients who suffered other diseases besides meningitis was measured by our sensitive enzyme linked immunosorbent assay for GM-CSF. The minimal detection level of GM-CSF was 40 pg/ml. Six of 9 patients (67%) with aseptic meningitis had detectable GM-CSF in cerebrospinal fluid and the concentrations of GM-CSF ranged from 49 to 114 pg/ml (mean 72 pg/ml), whereas none of 5 patients with bacterial meningitis or 6 patients with other diseases besides meningitis had detectable GM-CSF levels. There was no clear correlation between the GM-CSF levels in cerebrospinal fluid and the leukocyte count in either peripheral blood or cerebrospinal fluid, or the concentration of protein or glucose in cerebrospinal fluid.