OBJECTIVE: To investigate the clinical significance of detecting interleukin-6 (IL-6) and interleukin-12 (IL-12) in the immunological mechanism of hepatitis B virus infection (HBV). METHODS: Serum IL-6 and IL-12 levels were determined using enzyme-linked immunosorbent assay in patients with chronic, acute or advanced hepatitis B as well as in healthy subjects. RESULTS: In chronic, acute, severe hepatitis B patients, serum IL-6 levels were significantly elevated as hepatitis worsened (199.7+/-26.9, 129.5+/-22.8, 286.1+/-56.7 pg/ml respectively), in that order compared with the normal control levels (56.41+/-12.9 pg/ml). IL-12 levels, in contrast, tended to be lowered with the deterioration of hepatitis (24.6+/-13.4, 135.3+/-60.8, 19.7+/-9.0 pg/ml respectively), in that order, with the control level of 34.7+/-11.8 pg/ml. CONCLUSION: Serum IL-6 level is closely correlated to the degree of hepatocyte damage in hepatitis B, while IL-12 may be instrumental in the defense mechanism against HBV infection, and IL-12 level elevation can be indicative of hepatitis recovery.