Blood and cerebrospinal fluid (CSF) concentrations of cefmenoxime were determined either microbiologically or by means of HPLC in 20 children with proven or suspected bacterial meningitis. Sixteen children suffered from bacterial meningitis: causative organisms were Haemophilus influenzae type b (n = 10), Streptococcus pneumoniae (n = 4) and Neisseria meningitidis (n = 2). In these patients the cefmenoxime concentration in the CSF ranged from 0.9 to 12.2 mg/l, with a mean concentration of 4.63 mg/l 1.5-3 h after the last intravenous cefmenoxime application and 24-48 h after initiating therapy with 200 mg cefmenoxime/kg/d in four doses. In eight cases the bactericidal titers of the CSF were examined during therapy. Titers between 1:64 and 1:2,048, exceeding the minimal bactericidal concentration, were found. After five doses of cefmenoxime 50 mg/kg, two CSF cultures showed bacterial growth: one H. influenzae (bactericidal titer in CSF 1:256) and one S. pneumoniae.