The in vitro antibacterial activity of miocamycin was compared with four other macrolides (erythromycin, roxithromycin, josamycin, spiramycin) and pristinamycin against 90 clinical isolates of Branhamella catarrhalis by determination of minimum inhibitory concentrations. Sixty three strains were producing penicillinase. Fourteen carbons macrolides and pristinamycin are more effective than sixteen carbons macrolides. In this group, miocamycin have the best activity. There were no significant differences of susceptibility between penicillinase producing and non producing strains.