A total of 1246 clinical isolates ofHaemophilus influenzae from pediatric patients were recovered in Chiba Municipal Hospital. We studied the characteristics of these strains with regard to β-lactamase production and in vitro activities of antimicrobial agents between January 1995 and June 1997. Two hundred and ten strains (16.8%) of these isolates produced β-lactamase. Eight β-lactamase-positive isolates were resistant to amoxicillin-clavulanate (MICs, ≥12 μg/mL). Most of these were isolated from respiratory tracts. These strains were mainly cultured from boys less than 3 years old with chronic respiratory disease. Two strains were serotype b and 6 strains were not typeable. Some of these strains were eradicated without antibiotic treatment. Although the clinical impact of β-lactamase-producing and amoxicillin-clavulanate-resistantHaemophilus influenzae remains low, the number of infections caused by these strains may increase in the near future. We must monitor this tendency.