A rapid increase in the prevalance of beta-lactamase producing M. catarrhalis isolates has highlighted its pathogenic potential. In this study, we aimed to detect the BRO beta-lactamases of our clinical (n = 32) and carrier (n = 32) strains of Moraxella catarrhalis and compare the relationship of the enzyme type in assesment of MIC results of the antibiotics tested. BRO beta-lactamases were differentiated by restriction endonuclease analysis. Antibiotic susceptibility was performed by the agar dilution method recommended by NCCLS (M7A5). The clinical isolates produced 96.9%, whereas the carrier strains produced 90.6% beta-lactamase positivity by the restriction enzyme analysis. BRO-1 was isolated as 90.6% (n = 29) while the BRO-2 and non-beta-lactamase producers (NBLP) were isolated as 6.3% (n = 2) and 3.1% (n = 1) respectively among clinical isolates. The rate of BRO-1 in the carrier strains was 75.0% (n = 24), BRO-2 was 15.6% (n = 5) and NBLP was 9.4% (n = 3). The beta-lactamase production with nitrocefin test was 96.9% (31/32) in clinical isolates and 90.6% (29/32) in carrier strains. M. catarrhalis needs a continous monitoring of antibiotic susceptibility; in this era restriction endonuclease analysis could be useful to screen BRO beta-lactamase genes. © 2004 Taylor & Francis.