Seven cases of adult Haemophilus parainfluenzae infections diagnosed by positive blood cultures are compared with cases previously reported in the English literature. Three patients had pneumonia, while the others had epiglottitis with meningitis, pharyngitis, arthritis, and endocarditis, respectively. Nonendocarditic manifestations of adult H parainfluenzae infection were reported in four other cases. In addition to the diseases of our patients, H parainfluenzae also has been isolated from cerebral abscesses. Patients did well with antibiotic therapy and there were no deaths. Patients did well with antibiotic therapy and there were no deaths. Report of antibiotic sensitivity testing of 50 strains disclosed 6% of isolates resistant to ampicillin sodium, with all sensitive to chloramphenicol. If the antibiotic sensitivity of the organism is unknown, then chloramphenicol therapy should be instituted until adequate susceptibility studies have been performed. If the organism is sensitive to ampicillin, then this is the drug of choice.