Staphylococcus aureus and S. epidermidis are major causes of infection related to biofilm formed on indwelling medical devices. Such infections are common causes of morbidity and mortality and, because of biofilm resistance to antibiotics, are difficult to treat. The RNAIII-inhibiting peptide (RIP) (YSPWTNF-NH2) inhibits the pathogenesis of staphylococci by disrupting bacterial cell-cell communication (known as "quorum sensing"). Using a vascular-graft rat model, we show that RIP, applied locally and systemically, can completely inhibit drug-resistant S. aureus and S. epidermidis biofilms. The present study provides the first direct demonstration that interfering with cell-cell communication by use of a quorum-sensing inhibitor can eliminate medical device-associated staphylococcal infections. We suggest that medical devices could be coated with RIP to prevent infections, including those by antibiotic-resistant staphylococcal strains.