Streptococcal endocarditis has been well recognized for decades and over the years investigators at The New York Hospital have defined many of the diagnostic and therapeutic modalities currently employed in patients with this disease. In this study, speciation of the viridans streptococci has provided new insights into the relative frequency and antimicrobial susceptibility patterns of these organisms. Indeed, recent studies also suggest that S. milleri endocarditis is associated with a high incidence of suppurative complications and that patients with S. bovis endocarditis may have a significant incidence of underlying but asymptomatic lower gastrointestinal malignancies. Further studies correlating viridans streptococcal species with other clinical and laboratory parameters of endocarditis should provide additional insights into this disease.