Objective: To explore the effect of cellular immunity in halothane hepatitis. Methods: Hepatotoxicity model was established by exposing male Hartley guinea pigs to 1% halothane via inspiration for 4 h each time for 1 or 3 times within a 42-day interval. Then their hepatocytes and lymphocytes were collected and divided into 2 parts for different cultures. Hepatocytes were cultivated with or without 1% halothane for 4 h and lymphocytes were cultivated with or without 12.5 μg/ml trifluoroacetylated guinea pig serum albumin (TFA-GSA). Then the 2 kinds of hepatocytes were co-cultivated with lymphocytes (1:100) with or without TFA-GSA induction respectively and the supatant fluid was taken after 24, 48 and 72 h to determine the concentration of alanine aminotransferase (ALT). The halothane cultivated hepatocytes were co-cultivated with various proportion of TFA-GSA antigen induced lymphocytes and ALT was determined after 48 h to determine the proper proportion of hepatocytes and lymphocyte. Results: Lymphocytes of 3 times halothane induced guinea pigs caused a significant increase of ALT in hepatocytes with or without halothane induction. But the lymphocytes of l time halothane induced guinea pigs only caused a significant increase of ALT in hepatocytes with induction of halothane. The increase of ALT was only seen after 48- and 72-hour co-culture. The proper proportion of hepatocytes and lymphocytes was l:100 for lymphocytes cytotoxicity. Conclusion: Lymphocytes is sensitized after inhalation of halothane and generates cytotoxicity to hepatocytes. The immune response of lymphocytes to hepatocytes will be enhanced by repeated inhalation of halothane. The cellular immunity may be one of the mechanisms of halothane induced hepatotoxicity.