Granulocyte colony-stimulating factor (G-CSF) in the cerebrospinal fluid from patients with meningitis was measured by our modified enzyme-linked immunosorbent assay for G-CSF. The minimal detection level was 20 pg/mL G-CSF. In patients with bacterial meningitis, the G-CSF levels in the cerebrospinal fluid were extremely elevated, showing a mean value of approximately 1,500 pg/mL. On the other hand, G-CSF levels in the cerebrospinal fluid from 67% patients with aseptic meningitis were moderately increased, showing a mean value of about 80 pg/mL, whereas G-CSF levels in 33% samples remained undetectable. The G-CSF levels and neutrophil counts in the cerebrospinal fluid were proven to be related by Spearman's rank correlation coefficient analysis (r = .724). These elevations of G-CSF levels at inflammation sites associated with bacterial meningitis may indicate that G-CSF plays an important role in the combat of bacterial infections.