Pseudomonas aeroginosa exotoxin A(PEA) was purified from the strain PA103 and labelled with Ⅰ~(125).Then autoradiographic tracing,histopathological observations with light and electron microscopes,and antiserum protestion test were carried out on inbred mice BALB/C.The results indicate that the liver is the target organ of PEA,and both the hepatocytes and kupffer cells the target cells,on which the severe damage may be responsible for the acute death of the toxicated animals.