From August 1980 through July 1984, 19 neonates had sepsis due to Haemophilus influenzae. Onset of disease occurred within 48 hours after birth of all the neonates. One neonate was born at term and 18 were born prematurely, including seven neonates born before 28 weeks' gestation. Eight neonates and one fetus died, six of them within 24 hours of birth. Acute chorioamnionitis was present in the placentas. Those neonates with the most severe placental inflammation survived while all of those who died had moderate or only mild chorioamnionitis. Acute villitis was noted in the placentas of three neonates who died. Respiratory distress syndrome (in 15 neonates) and pneumonia (in 15 neonates) were noted in 18 liveborn patients. Nine mothers had fever, six of them with genitourinary infections and one with septicemia due to H influenzae. All isolates of H influenzae were submitted for serologic typing and none were typable. In 14 cases, isolates were biotyped yielding eight with biotype II, four with biotype III, and one each with biotypes IV and V. Neonatal sepsis due to nontypable H influenzae is now nearly as common as sepsis due to group B Streptococcus. Both organisms produce diseases with many features in common, especially fulminant courses with respiratory distress and pneumonia, and often have a fatal outcome.