Three cases of endocarditis due to nutritionally deficient (variant) streptococci are presented and the literature is reviewed. In all of the cases reviewed, the patient presented with an indolent subacute course. Prior heart disease was present in 90% of the patients, embolization occurred in 27%, relapse after therapy in 17%, and death in 17%. Bacteriologic failure occurred in 41% of cases, despite sensitivity of the organisms to the antibiotics used in two-thirds of these cases. Combination therapy with penicillin and an aminoglycoside has been recommended previously; however, in 38% of the cases reviewed, bacteriologic failures occurred and the patients required surgery. The results of in vitro antibiotic-sensitivity testing are difficult to interpret and to apply to the expected response to therapy. Further studies on these organisms are needed to reduce the high rates of failure, relapse, and fatality.