Cholesterol may interfere with normal repair processes in the arterial wall. It is also possible that this same action occurs during inflammation and repair throughout the body. This hypothesis was tested by giving intravenous injections of Bacteroides fragilis, a bacterium that is innocuous for normal rabbits even when multiple large doses are given. Almost all cholesterol-fed rabbits developed significant pleuropulmonary infections with complications that included vasculitis, thrombosis, extrapulmonary infections, and significant mortality. More than half of this group was culturally positive for B. fragilis at the time of autopsy while cultures from control animals were sterile. These results suggest that cholesterol may interfere with the functions of those cells involved in host defense.