The newest group of macrolides are semisynthetic compounds known as ketolides. These compounds are the focus of considerable interest, particularly for activity against several erythromycin-resistant species, including Streptococcus pyogenes, Streptococcus pneumoniae, Staphylococcus aureus and some Enterococci. Two ketolides are in Phase II clinical trials. The author discusses the potential for this new class of compounds in an environment of growing microbial resistance to existing antibacterial agents.