Corynebacterial endocarditis is an uncommon disease. In 1951, only eight examples were listed by Jones 1 in a review which covered 349 reported instances of endocarditis of nonstreptococcal origin. In 1964, however, no fewer than 26 cases were mentioned by Prévot2 in a survey of the pathologic manifestations of anaerobic corynebacteria. Since the pathogenicity of certain strains of diphtheroids is currently being studied in this laboratory, it seemed worthwhile to review cases of bacterial endocarditis diagnosed in the Cleveland Metropolitan General Hospital to see if any had been due to corynebacteria. At the same time, the literature from 1949 onward was critically reviewed to ascertain how frequently this type of endocarditis had been reported since Jones' review and to examine the evidence incriminating a group of organisms which is generally regarded as nonpathogenic. Results Examination of hospital charts and pathology department autopsy files over the years 1949 to 1963