Staphylococci inoculated intravenously into dogs with and without aortic insufficiency (Al) were recovered in large numbers one hour later from spleen, liver, lung, kidney, adrenal glands, and myocardium, but not heart valves. By 18 hours, numbers declined by approximately 2 logs in spleen, liver, lung, and adrenal, but increased in kidney and myocardium. Staphylococci were recovered from most aortic and mitral valves of dogs with Al at 18 hours, and continued to proliferate and cause endocarditis. Only low grade colonization occurred in pulmonary and tricuspid valves. Valves of normal dogs were sterile 1, 18, 44 hours, and one week after inoculation. After 18 hours, staphylococci decreased in all tissues of normal dogs except kidneys. Contrariwise, in dogs with Al they increased in all tissues. Endocarditis and myocarditis occurred in dogs with Al but not normal dogs. Infectious lesions were otherwise similar in the two groups, though more frequent in the