Between 1976 and 1981 Haemophilus influenzae was identified in 16 women with postpartum bacteremia and 36 neonates with bacteremia or meningitis. H. influenzae was also recovered from neonatal or genital cultures of 50 additional patients. By counter-immunoelectrophoresis 17% of neonatal isolates from blood or cerebrospinal fluid (CSF) were type b. All remaining strains (94% overall) were nontypable (NT). Of the NT blood or CSF isolates, 38% belonged to biotype 4. Of all the NT biotype 4 isolates referred to the Centers for Disease Control during the study, 82% were of genital, neonatal, or maternal origin, a finding that suggests that this isolate is a genital biotype. Clinical disease was similar to that observed in patients infected with group B Streptococcus except for the infrequent (11%) occurrence of meningitis. Maternal bacteremia resulted in mild febrile illness, while neonatal bacteremia was associated with a high incidence of shock, respiratory distress (50%), and death (30%). H. influenzae bacteremia in these two patient groups was rare in Houston before 1976, but since then it has been responsible for 2.5% of cases of significant bacteremia. NT H. influenzae should be recognized as a definite neonatal, maternal, and genital pathogen.