To study the sequential changes of serum ferritin levels in lamivudine-treated patients with chronic viral hepatitis B and the clinical implications. Thirty-eight patients with chronic viral hepatitis B were prospectively studied during their treatment with lamivudine. Each patient received 100 mg oral lamivudine daily for 12 mo, and was observed and tested for blood biochemistry and hepatitis B virus (HBV) DNA levels and serum ferritin levels at baseline and at 3, 6 and 12 mo during the treatment. Serum HBV DNA levels were quantitatively determined using fluorescent quantitative polymerase chain reaction (FQ-PCR), and serum ferritin levels were measured by radioimmunoassay. The sequential changes of serum ferritin levels and their relationships with virological, serological and biochemical responses in the patients were analyzed. All the patients had a baseline HBV DNA level higher than 1 x 10(7) copies/L as determined by FQ-PCR and positive HBsAg and HBeAg and abnormal ALT levels. At the end of the 12-mo treatment, 19 of the 38(50.00%) patients had undetectable serum HBV DNA levels by FQ-PCR, and 12(31.58%) became negative for serum HBeAg and 10(26.32%) had seroconversion from HBeAg to HBeAb. Nineteen out of the 38(50.00%) patients had biochemically normal ALT levels after 12-mo lamivudine treatment. Sequential determination showed that lamivudine treatment significantly reduced ferritin levels in chronic hepatitis B patients. When the patients were divided into different groups according to their post-treatment virological, serological and biochemical responses for analysis of the sequential changes of ferritin levels, it was found that the decrease of ferritin levels in HBV DNA-negative group was significantly more obvious than that in HBV DNA-positive group at 6 mo during the treatment (P=0.013). Consecutive comparisons showed that ferritin levels at 3 mo of treatment were obviously decreased as compared with the baseline levels (P<0.05) in HBeAg-negative group, and the decrease of serum ferritin levels in patients with normalized ALT was more significant than that in patients with abnormal ALT at the end of the 12-mo treatment (P=0.048). Lamivudine treatment can reduce the serum ferritin levels in chronic viral hepatitis B patients and decreases of ferritin levels can be more significant in patients exhibiting virological, serological and biochemical responses, indicating that dynamic observation of serum ferritin levels in patients with chronic viral hepatitis B during lamivudine treatment might be helpful for monitoring and predicting patients' responses to the therapy.