Eleven children with bacterial meningitis were treated intravenously with amoxicillin sodium to evaluate the efficacy of the parenteral form of amoxicillin for this serious infection and to measure the penetration of the drug into cerebrospinal fluid (CSF). The infecting organisms were Haemophilus influenzae in nine cases and Streptococcus pneumoniae in two. Nine patients had optimal responses to amoxicillin sodium, 200 mg/kg per day for 14 days. Bacteria were also eradicated from CSF of the other two, but one experienced fever and culture-negative CSF pleocytosis after cessation of amoxicillin, and the other developed H. influenzae empyema 2 weeks after termination of therapy. By comparison, 7 of 10 children with meningitis responded optimally to ampicillin (nonrandomized design) during the period of study. The mean peak CSF concentration of amoxicillin was 3.14 mug/ml (ca. 7% of the concomitant mean peak serum level) early during therapy. However, meningeal penetration of the drug declined to a mean peak of 0.63 mug/ml on the final day of therapy. Mild transient neutropenia, noted in five patients, was the most common side effect of amoxicillin sodium therapy; five patients treated with ampicillin also experienced reversible neutropenia. Thus, intravenous amoxicillin sodium provided therapy for bacterial meningitis comparable to that of ampicillin in this limited case-control study.