The combination of ampicillin with either gentamicin or chloramphenicol, which is currently the initial chemotherapy for purulent meningitis, has lost its effectiveness in recent years because of an increase in the incidence of ampicillin-resistant strains. This has made it necessary to search for a suitable substitute therapy.Twenty-two new P-lactam agents were compared with penicillin G and ampicillin in terms of their antibacterial activity in relation to the principal causative microbes of meningitis and their ability to transfer into the cerebrospinal fluid (CSF) of rabbits with experimental staphylococcal meningitis. In addition, a survey was conducted of the therapeutic efficacy achieved by these drugs in cases seen by the authors and in other domestic and overseas cases. Finally, an investigation was made as to whether or not the transfer of the drug into the CSF was suppressed when it was administered simultaneously with ampicillin.From the results, it was surmised that in future the most appropriate initial chemotherapy for purulent meningitis will be a combination of cefotaxime, or perhaps ceftriaxone, plus ampicillin.