Five cases of pneumonia due to H. influenzae Type b are reported. Three were in infants, 1 in a 5-year-old boy and the fifth in a 62-year-old man. The consolidations in all were lobar or segmental in distribution, and pleural effusions occurred in 3 patients. Diagnosis was by growth of the organism in pure culture from the blood in 4 and from the lung at autopsy in 1. In 2 cases favorable therapeutic response was obtained with penicillin therapy, but in both streptomycin was added to the regimen following specific bacteriologic diagnosis. The nature of this infection is discussed, and the value of routine admission blood cultures in its diagnosis emphasized. In treatment of H. influenzae Type b infections it is recommended that a combination of 2 antibacterial agents to which the organism isolated is found susceptible be used and that one of these be chloramphenicol or streptomycin.