The concentrations of ceftazidime in the serum and cerebrospinal fluid of patients with and without meningitis were measured at various times after a 2- or 3-g dose. At similar concentrations in serum, ceftazidime concentrations in cerebrospinal fluid at a given time were substantially lower in patients without meningitis (mean, 0.8 micrograms/ml) than in those with meningitis (mean, 22.6 micrograms/ml).