Germfree and ordinary laboratory rats of the same strain, half of each sort treated with oral aureomycin for 3 days prior to shock, were subjected to hemorrhagic shock. At the level and duration of hypotension selected, the procedure was highly lethal for all four groups. The single survivor was not a germfree rat. No evidence was found for protection against fatal outcome by either germfree status or treatment with aureomycin, and the gross pathological changes seen at autopsy following death from shock were essentially similar in all groups. The volumes of blood shed, the times spontaneous uptake of blood began, and the volumes of uptake did not differ significantly among the groups. It is concluded that bacteria and bacterial products are not essential for the development of irreversibility in hemorrhagic shock as customarily produced in rats.