We conducted several studies using a combination of sulbactam (SBT) and cefoperazone (CPZ) in a ratio of 1:1 with the following results. Serum and cerebrospinal fluid (CSF) concentrations of the drugs were determined in 2 rabbits with meningitis caused by S. aureus. Following intravenous injection, serum concentrations of CPZ were higher than those of SBT in both rabbits whereas CSF concentrations were much higher with sulbactam than with CPZ indicating good penetrability of SBT into CSF. The serum concentration of SBT at 1/2, 1, 2 and 4 hours after an intravenous administration of 9.8 mg/kg of the combination to a child were 3.5, 1.4, 0.3 and 0.1 microgram/ml and those of CPZ 19.0, 13.0, 6.7 and 2.9 micrograms/ml, respectively. The half-lives were 0.705 hours for SBT and 1.31 hours for CPZ. An intravenous dose of this combination (19.6 mg/kg) was given 3 times a day to 13-year-old girl with decreased neutrophil chemotaxis due to periblepharal abscess caused by S. aureus. The therapeutic effect was excellent. Though very slight transient eosinophilia was noted, no adverse reaction was found. The susceptibility of the isolated organism to this drug was not determined, but it was found to be resistant to the CTX using the disc method.