Three fatal cases of listerial endocarditis were studied. The first case occurred in an apparently healthy 58-year-old man, who presented with symptoms of pneumonitis. The second case developed in a 75-year-old woman with adenocarcinoma of the lung and aortic stenosis. In the third patient, an 83-year-old woman, aortic valve vegetations with perforations were found at necropsy. A colonic adenocarcinoma was found in the first and third cases. Ampicillin, alone or with an aminoglycoside, was the antibiotic used. Urgent valve replacement was performed in the first case. Listeria monocytogenes was isolated from blood cultures in all three cases. A review of 41 other patients with listerial endocarditis showed a nonspecific clinical picture, but septic complications occurred in one-half of the cases. Thirty-nine patients had at least one predisposing factor, which was underlying heart disease in 25 cases. The mortality rate was 48%.