SummaryOne hundred eighty consecutive, unduplicate isolates ofHaemophilus influenzaefrom clinical specimens collected from November 1994 through February 1995 in nine general hospitals throughout Belgium were examined for p-lactamase production using a nitrocefin-based test, and for theirin vitrosusceptibilities to ampicillin, amoxycillin/clavulanate, cefaclor, cefuroxime, cefotaxime, clarithromycin and azithromycin by means of the NCCLS agar dilution test. The isolates were all from respiratory tract specimens. The prevalence of capsular type b was 1.1 %, and the overall rate of p-lactamase production 16.7%. Rates of P-lactamase production were higher in isolates from children (22.0%) than in those from adults (15.3%), and in isolates from upper respiratory tract specimens (22.0%) than in those from the lower resj Piratory tract (15.1%). Beta-lactamase-negative ampicillin resistance amounted to 1.1%. Cefotaxime had the highest activity on a weight basis [MIC (minimal