Sixteen hospitalized patients, aged between 10 and 76 years (mean: 34.3 years), with bacterial meningitis were treated i.v. with cefoperazone at daily doses of 4.5 g to 9 g. In two cases ampicillin was given in combination with cefoperazone during the last four days and the first five days of treatment, respectively. The following organisms were isolated: Neisseria meningitidis (n = 9), Haemophilus influenzae (n = 3), Escherichia coli (n = 2), Streptococcus pneumoniae (n = 2). Fourteen patients completely recovered from infection and the pathogens were eradicated; the treatment failed in only two patients and both were cured with alternative treatment. Furthermore, in 11 patients cefoperazone serum and CSF levels were determined four times during the first week of treatment (1st, 3rd, 5th and 7th days). No important side effects were recorded.