BACKGROUND Hepatitis B is a global health problem. Use of complementary and alternative medicine has been popular among patients with hepatitis B. This 1-year open-label pilot study aims to observe whether Agaricus blazei Murill extract improves liver function in patients with hepatitis B. METHODS This study involved 12 months of clinical observation. Four (4) patients with hepatitis B who met the criteria (1) aged between 20 and 65 years; (2) being Chinese; (3) having been a hepatic B carrier (HBAg(+)) for more than 3 years; (4) alanine aminotransferase > 100 IU/L; and (5) not taking lamivudine, alpha-interferon, or other drugs for hepatitis participated in the study with informed consent. The enrolled patients were given Agaricus blazei Murill (ABM) extract of 1500 mg daily for 12 months. The level of alanine aminotransferase was taken as the major outcome measurement. RESULTS At the end of the study, the mean level of aspartate aminotransferase and alanine aminotransferase decreased from 246.0 (+/- standard deviation [SD] 138.9) to 61.3 (+/- SD 32.6) IU/L and 151.0 (+/- SD 86.9) to 46.1 (+/- SD 22.5) IU/L, respectively. CONCLUSIONS Our initial observation seems to indicate the potential benefit of ABM extract in normalizing liver function of patients with hepatitis B. Controlled studies with larger samples should be conducted in the future.