A study has been made of 12 patients with pneumococcal meningitis with ages ranging from 12 months to 59 years. In all cases pneumococcus was isolated in the cerebrospinal fluid (CSF). Seventeen pneumococci were studied for their sensitivity to fosfomycin, ampicillin and gentamicin, including their MIC. All were sensitive to fosfomycin and ampicillin and 7 to gentamicin. On the other hand there has also been made a study of the interaction between fosfomycin plus ampicillin and fosfomycin plus gentamicin. The concentration of antibiotics in plasma and CSF had been determined. The association of fosfomycin to penicillin or ampicillin was also studied in some cases, depending on whether the patient was younger or older than 2 years, and in other cases, the association of fosfomycin with gentamicin. The concentrations of antibiotics in the CSF varied according to the stage of evolution of the meningitis. As regards clinical results, 10 cures and 2 failures have been obtained. The pneumococcus was eradicated from the CSF in all cases, including the two failures, in the control carried out 2–3 days after beginning of treatment, the rest of the analytical data of the CSF became normal within 5 and 17 days treatmen