Fifty-six patients with enterococcal endocarditis received 4 weeks of antimicrobial therapy with penicillin G and streptomycin (36 patients) or, if infections were streptomycin resistant, penicillin and gentamicin (20 patients). Compared with patients who had symptoms for less than 3 months, patients with symptoms for more than 3 months had a higher relapse rate (0% versus 44%; p less than 0.001) and mortality (2.5% versus 25%; p less than 0.001). Patients with mitral valve endocarditis had a significantly higher relapse rate (25%) than patients with aortic valve infections (0%) (p less than 0.01). Gentamicin-associated nephrotoxicity was more frequent (p less than 0.001) among patients treated with greater than 3 mg/kg d of gentamicin than among those treated with 3 mg or less (100% versus 20%). Relapse and mortality rates did not differ significantly between patients treated with low-dose or high-dose gentamicin regimens. Patients who have had symptoms of enterococcal endocarditis for more than 3 months or patients with mitral valve infection should receive at least 6 weeks of antimicrobial therapy, but patients without these high-risk factors can be treated for 4 weeks.