Forty-six hospitalised patients with respiratory tract infections (RTI) in whom Branhamella catarrhalis had been isolated were evaluated. On average they were 70 years old, there were 39 males and 7 females, 89% of them were smokers. In 85% Branhamella catarrhalis caused exacerbation of chronic bronchitis and in 15% the pneumonia. Most cases of this infection were detected in December and January. In vitro 78% of strains formed beta lactamasis. All 46 isolations were sensitive to cyprofloxacin, 43 (93%) to the combination of amoxicillin with clavulanic acid, 41% (89.1%) to erithromycin, 44 (95.6%) to gentamycin and only 26 (56.5%) to trimetoprim-sulphametoxasol. In the therapy amoxicillin with clavulanic acid, macrolids and kinolons were successful while trimetroprim-sulphametoxasol was less effective.