Ultrastructural studies on liver cell necrosis and the interaction of lymphocyte and liver cell were carried out in experimental hepatitis B in chimpanzees. Two types of liver cell necrosis were identified. One was a lytic necrosis, and the other was a coagulation necrosis. Both types of liver cell necrosis were closely associated with the apposition of lymphocytes. The interaction (or close contact) of lymphocyte and non‐necrotic liver cell infected with HBV was also detected. There were two distinct patterns of the contact. One was the direct contact, and the other was the contact with the intervention of electron‐dense fuzzy material containing 20 to 22 mu spherical particles and 51 to 55 mu double‐layered spherical particles. The ultrastructural characteristics of lymphocytes in each pattern of the contact were different. The results suggested that the pathogenesis of liver cell necrosis in hepatitis B was closely associated with the action of lymphocytes, and two modes of lymphocytic reaction were conceivable. ACTA PATHOL. JPN. 35 : 1359 ‐1374, 1985.