OBJECTIVE To investigate the ability of serum procalcitonin (PCT) to differentiate between bacterial and viral meningitis. METHODS The serum PCT levels were measured in 41 children with acute bacterial (n=18) or viral (n=23) meningitis by immunoluminometric assay. Meanwhile serum CRP levels and erythrocyte sedimentation rate (ESR) were measured. RESULTS The children with acute bacterial meningitis had higher levels of PCT (51.73 +/- 30.75 microg/L) and CRP(182.36 +/- 54.5 mg/L) and ESR (50.44 +/- 8.95 mm/h) than those with viral meningitis (0.84 +/- 0.99 microg/L, 8.90 +/- 10.66 mg/L and 16.75 +/- 13.23 mm/h respectively, P < 0.01). Both PCT and CRP had high predictive value for bacterial meningitis based on the area under curve of the receiver operating characteristics curves, 0.984 for PCT (95% confidence interval 0.953-1.013) and 0.983 for CRP (95% confidence interval 0.954-1.012) (P > 0.05). All of the children with bacterial meningitis had serum PCT levels above 0.5 microg/L, but only 2 patients with viral meningitis exceeded this value. CONCLUSIONS The measurement of serum PCT levels may be of value in the differential diagnosis of meningitis due to either bacterial or viruses.