Haemophilus aphrophilus is a fastidious gram-negative bacillus found in mouth of normal individuals. Though H. aphrophilus infection is quite rate, it includes such serious ones as endocarditis and brain abscess. The authors isolated H. aphrophilus from five patients with the diagnosis of lung abscess, conjunctivitis, brain abscess and facial masticator space abscess. Two of the patients died. Three of the patients also yielded other species of bacteria from the same specimens. One of the isolate was intermediately susceptible to amikacin and resistant to tobramycin, indicating the necessity of a routine susceptibility test in order to select the proper antimicrobial agents. Since H. aphrophilus can be differentiated from other similar organisms by morphological and biochemical characteristics, one should determie the possibility of this organism when fastidious gram-negative bacilli are isolated from blood or from sites adjacent to upper respiratory tract.