Eighteen medium-sized mongrel dogs were used to study experimental enterococcal endocarditis. Aortic valve Injury was accomplished by needle punctures through a catheter in the left carotid artery. Thirteen dogs survived the procedure and one week later received a suspension of 107enterococci intravenously. In 10 dogs a sustained bacteremia of 102organisms per milliliter of blood or greater occurred within one week and rose to 103in all but one animal shortly before death or sacrifice. Necropsy was performed in the dogs from 3 to 103 days after inoculation. Vegetative endocarditis involving both aortic and mitral valves occurred in 9 of 10 canine subjects. Bacterial counts on affected valves ranged from 107to 109per gram of tissue. Thromboembolic and hemorrhagic lesions were noted in the kidneys, myocardium, spleen, and lungs. The simplicity of this technique should prove this a useful model for therapeutic and patholophysiologic studies.