BACKGROUND: High-level aminoglycoside resistance (HLAR) that precludes bactericidal synergism with penicillins or glycopeptides and nephrotoxicity related to aminoglycoside treatment are major problems in treating Enterococcus faecalis endocarditis. OBJECTIVE: To evaluate the efficacy and safety of ampicillin plus ceftriaxone for treating endocarditis due to E. faecalis with and without HLAR. DESIGN: Observational, open-label, nonrandomized, multicenter clinical trial. SETTING: 13 centers in Spain. PATIENTS: 21 patients with HLAR E. faecalis endocarditis and 22 patients with non-HLAR E. faecalis endocarditis. All were at risk for nephrotoxicity related to aminoglycoside use. INTERVENTION: 6-week course of intravenous ampicillin, 2 g every 4 hours, plus intravenous ceftriaxone, 2 g every 12 hours. MEASUREMENTS: Clinical and microbiological outcomes. RESULTS: The clinical cure rate at 3 months was 67.4% (29 of 43 patients) among all episodes. During treatment, 28.6% of patients with HLAR E. faecalis endocarditis and 18.2% of patients with non-HLAR E. faecalis endocarditis died of infection-related causes. The rate of clinical and microbiological cure in patients who completed the protocol was 100% in the HLAR E. faecalis endocarditis group. No episodes of breakthrough bacteremia occurred, although there were 2 relapses in the non-HLAR E. faecalis endocarditis group. Treatment was withdrawn in 1 case because of fever and skin rash. LIMITATIONS: The study had a small sample and was observational. CONCLUSION: The combination of ampicillin and ceftriaxone is effective and safe for treating HLAR E. faecalis endocarditis and could be a reasonable alternative for patients with non-HLAR E. faecalis endocarditis who are at increased risk for nephrotoxicity.