A normal full-term baby boy, born by vaginal delivery, became ill on day 2 with fever and failure to feed. CSF examination revealed 260 x 10(6)/l leucocytes, mainly mononuclears, protein 2 g/l and glucose zero. Pasteurella multocida was isolated in pure culture from the baby's CSF, blood and umbilicus and from the mother's vagina. The baby was treated with i.v. penicillin for 7 weeks. Progress was complicated by mild hydrocephalus, which resolved, and prolonged low grade fever. Recovery was complete, without neurological sequelae. This case illustrates that P. multocida can infect the vagina where it presents a hazard to a newborn infant delivered vaginally. Early diagnosis is critical, intravenous high dose penicillin being the treatment of choice.