Epidemiological and microbiological studies were carried out using 575 strains of Haemophilus influenzae isolated from clinical specimens at Kitakyushu municipal medical center from January 1996 through December 1999. The strains isolated multiply were excluded. The strains of H. influenzae did not increase for 4 years, and were detected more in summer season, peaked in July, and less in winter season. Like the cases of Streptococcus pneumoniae, most (91.8%) of the strains was detected in the specimens from the respiratory tract, and also they were isolated mainly from infants under 4-years old (25.6%) and adults over 65-years old (24.2%) MICs of 7 antimicrobial agents, such as ampicillin (ABPC), sulbactam/ABPC, cefaclor, imipenem, panipenem, meropenem (MEPM), and levofloxacin (LVFX) were determined using broth microdilution methods. Among 575 strains of H. influenzae isolated from clinical specimens, 51 ABPC-resistant strains (8.9%) produced beta-lactamase, and 67 strains (11.6%) were beta-lactamase negative ampicillin resistant H. influenzae. The ABPC-resistant strains existed in 20.5%. Both of MEPM and LVFX showed excellent antimicrobial activity against H. influenzae including ABPC-resistant strains. Four cases of meningitis were reviewed. All of H. influenzae isolated possessed type b capsular antigen. All patients recovered by appropriate antimicrobial treatment. But one adult patient developed serious sequela.