Ceftazidime is active in vitro against Haemophilus influenzae. When given to infant rats in a dose of 25 mg/kg ceftazidime achieved a mean peak blood concentration of 31.8 mg/l and a mean trough concentration at 3 h of 25 mg/l during steady state. Blood half-life of ceftazidime was 1.3 h. Mean CSF penetration of ceftazidime was 22.8% of blood levels, independent of the presence or absence of meningitis. Infant rats with meningitis due to beta-lactamase negative and beta-lactamase positive H. influenzae strains had decreased CSF bacterial counts 8 h after a single 25 mg/kg dose and, without additional therapy, 45% of animals maintained negative cultures.