Recent studies have suggested that combination antibiotic therapy is preferable to monotherapy for severe community-acquired pneumonia (CAP). In this issue Mortensen and colleagues present retrospective data suggesting that combination therapy with a cephalosporin and a fluoroquinolone is inferior to combination therapy with a cephalosporin and a macrolide. Several mechanisms exist by which quinolones could be inferior to macrolides in combination therapy, so if these findings are confirmed by other groups they have significant implications for physicians treating patients with severe CAP.