Thirty-one cases of bacterial endocarditis in adult dairy cows were reviewed. Clinical signs were reflective of the stage of the disease. Recurrent or persistent fever, tachycardia and a pounding heartbeat or systolic murmur, polypnea, and lameness were typical. With chronicity, weight loss and poor production developed. The end stage was congestive heart failure. Neutrophilia was typical in early cases. Low-grade anemia and high total serum globulin content developed with chronicity and seemed to be negative prognostic signs. Corynebacterium pyogenes was the organism most frequently identified by blood culture or at necropsy. Twenty cows were necropsied and 2 cows were sent to slaughter. Nine cows in which the diagnosis was made early in the course of the disease responded to long-term penicillin therapy.