Hemolysin, cell-free autolysate, and lipopolysaccharide (LPS) prepared from Escherichia coli (O141) were parenterally administered to 113 weaned pigs. Both the hemolysin and the cell-free autolysate were crude preparations which probably contained several biologically active substances. Pigs in all groups which die less than 72 hours after injection had similar gross and microscopic lesions. The pigs which survived (chronically affected pigs) were killed 3 to 12 days after injection. Of the pigs that lived more than 72 hours after injection, those given hemolysin and autolysate had generalized vascular myolysis and fibrinoid necrosis, whereas those given LPS had morphologically normal blood vessels. The vascular changes produced by hemolysin and autolysates of E coli (O141) were the same as the histologic angiopathy of naturally occurring edema disease of pigs. The LPS produced acute lesions of endotoxin shock in the pigs, but did not produce the angiopathy characteristic of edema disease. Typical clinical signs of naturally occurring edema disease were not a consistent observation in any of the treatment groups.