A penicillin-aminoglycoside regimen is accepted therapy for enterococcal endocarditis, but use of combinations of antibiotics in other forms of bacterial endocarditis is controversial. This review analyzes in-vitro, experimental animal model, and clinical studies of combination "synergistic" antibiotic treatment for enterococcal, viridans streptococcal, staphylococcal, and gram-negative aerobic bacillary endocarditis. Current recommendations for treatment of these entities are discussed.