With the purpose to elucidate the clinical significance of the so-called liver auto-antibody and heterophile antibody by means of Paul-Bunnell's reaction, the author studied histologically 138 cases of liver diseases including infectious hepatitis with liver biopsy specimens; and obtained the following results. 1. Those liver diseases in which the liver auto-antibody can be detected are infectious hepatitis, chronic infectious mononucleosis, and lupus erythematodes, and in addition, there are fatty liver, hepatoler ticular degeneration (Wilson's disease), mechanical jaundice, Banti's syndrom, and hepatoma; and all the liver auto-antibody of them start from necrotic destruction of liver tissue. 2. The liver auto-antibody titer were well correlated with the proliferation of interstitial connective tissue, exsudation in sinusoid, liver cell necrosis, and stellate cell activation, but have poor correlation with the portal cell infiltration and degeneration of liver cells. 3. Active chronic infectious hepatitis that later develops to liver cirrhosis, cholangiolitic hepatitis, and a portion of the chronic infectious hepatitis in which inflammation spreads to portal and periportal region show a high liver auto-antibody titer which persists for a long period of time. However, in such diseases as active chronic epidemic hepatitis or in serum hepatitis (posttransfusion hepatitis), the possibility of the liver auto-antibody becoming an endogenous factor to spread the local tissue changes to wider area is doubtful in the former, but it markedly strong in the latter. 4. It has been confirmed that heterophile antibody is produced by viral infection in infections hepatitis. Especially high agglutination titer can be found in posthepatitic liver cirrhosis and parenchymatous form of chronic infectious hepatitis, and assuming those titer over 40 times to be agglutination positive, it also has patho-histologically a clinical significance.