A retrospective analysis of data from 18 clinical studies was performed to examine the effectiveness and safety of cefaclor in the treatment of upper and lower respiratory tract infections caused byMoraxella catarrhalis(previously calledBranhamella catarrhalis)Eighty-six percent of 56 evaluable patients had improvement in their symptoms of infections following therapy with cefaclor. There were no serious or life-threatening adverse drug experiences reported by any patient. Cefaclor appears to be an appropriate antibiotic for the safe and effective treatment of respiratory tract infections caused byM. catarrhalis.