Regimens for endocarditis caused by these bacteria are generally based on high dosage of a β -lactam antibiotic, penicillin in the case of streptococci and a penicillinase-resistant penicillin for Staphylococcus aureus , with vancomycin substituted for β -lactam resistant staphylococci, including coagulase-negative staphylococci. The addition of other antimicrobial agents, such as aminoglycosides (or, in the case of staphylococci, sodium fusidate or rifampicin) may increase bactericidal efficiency, or allow shorter courses, but problems of toxicity or emergence of resistance may occur. Optimal regimens are discussed, and newer agents of possible usefulness are reviewed.