Results obtained during experiments on rats intoxicated with Gramoxone herbicide containing 25 per cent paraquat are reported using light- and electron microscopic examinations. The development of the liver's lesion may be divided into three phases: in the first phase predominates the destruction of the cytoplasmic organella in the hepatocytes, in the second one the proliferation of the Kupffer cells and in the third one the lesion of the biliary region. The regeneration is slower than in case of a healthy liver: the hepatic parenchyma is recovering at first and only later the epithelium of the bile ducts. The mechanism of action of the paraquat intoxication is discussed.