Interferon antibodies may negate the antiviral effects of recombinant alpha-interferon treatment in patients with chronic hepatitis B virus infection. In a randomized controlled trial of recombinant alpha-2a interferon for chronic hepatitis B, interferon antibodies developed in 21 (39%) of 54 Chinese adults who received IFN. No correlation was observed between sex, age, pretreatment serum ALT level or liver histological findings and the development of interferon antibodies. Antibodies were significantly more likely to develop in patients who received lower doses (2.5 or 5 MU/m2) of alpha-2a interferon than in those who received a higher dose (10 MU/m2): 53% vs. 11% (p = 0.006). The development of interferon antibodies appeared to reverse the initial antiviral response to treatment, with reappearance of hepatitis B virus DNA in serum in 12 patients and HBeAg in three patients. Sustained clearance of HBeAg was achieved in only one (5%) patient but was achieved in seven (21%) patients without interferon antibodies. The mere presence of interferon antibodies did not preclude an antiviral response to interferon therapy, but patients with high titer neutralizing antibodies were less likely to respond. These findings suggest that interferon antibodies may negate the antiviral effects of alpha-2a interferon. A higher incidence of interferon antibodies in Chinese vs. white patients with chronic hepatitis B may contribute to the poorer antiviral response in Chinese patients. 