Clindamycin was used to successfully treat a lung abscess caused by Legionella pneumophila. The activity of clindamycin, erythromycin, and rifampin against cell-associated growth of L. pneumophila in human monocytes was determined by broth time-kill methodology. More killing of cell-associated growth of L. pneumophila was achieved with clindamycin than with erythromycin. Synergy with rifampin was demonstrated with both erythromycin and clindamycin.