Coliform-free rabbits fed P(32) labeled E. coli 0111B(4) prior to the induction of experimental hemorrhagic shock were shown to have a substantial amount of the type-specific 0111B(4) antigen in the circulating blood, liver, and spleen, whereas normal rabbits fed the same amount of these bacteria and held under identical conditions, but not exposed to shock, have the antigen within the liver, and occasionally in the kidney, but not in the blood. That the antigen recovered from the blood and tissues was derived from this specific strain of bacteria was demonstrated by the use of the hemagglutination inhibition reaction, by the absence of cross-reacting antigens in appropriate control animals, and by agreement in the amount of antigen as estimated by two different technics. Transport of bacterial endotoxin across the intestinal membrane appears to be achieved primarily by passive diffusion. The accumulation of biologically active endotoxin in the blood and tissues of the shocked animal appears to be due to a reduction in the detoxifying potential of the reticulo-endothelial system, and not to a greater than normal absorption of endotoxin from the intestine. The absence of toxicity in the specific antigen extracted from normal liver demonstrates that the degradation of endotoxic potency can be achieved without altering the chemical integrity of the polysaccharide moiety of the molecule. The implications of the hypothesis that there is a continuous but fluctuating absorption of bacterial endotoxin from the intestine are briefly discussed, and the contribution of free circulating bacterial endotoxin of intestinal origin to the fate of the shocked animal is noted.