Hepatotoxicity study of the nitrosamine produced by interaction between drugs containing amino groups and soduim nitrite was conducted. In the in vitro study, interaction of 32mM Promethazine HCL or Oxomemazine HCL with 200mM Sodium nitrite produced N-nitroso dimetylamine (NDMA) at 0.4% or 0.03%, respectively. When sodium nitrite was administered with Promethazine HCL or Oxomemazine HCL, trace of NDMA was detected from the gastric contents. After three days of consecutive administration of sodium nitrite with Promethazine HCL or Oxomemazine HCL, the levels of GOT, GPT and SDH in the serum of treated groups were significant higher than that of control group.