Combination therapy between two immunomodulators used for treatment of chronic hepatitis B was explored based on reported therapeutic efficacy of interferon-alpha, and thymosin-alpha1 as monotherapeutic agents to determine if combination therapy was superior to interferon alone. This double-blinded, randomized, placebo-controlled trial compares the addition of thymosin-alpha1, 1.6 microg taken three times per week (combination therapy) or thymosin placebo (monotherapy) to lymphoblastoid interferon (Wellferon), 5 million international units (MIU) taken three times per week, for 24 weeks. Entry criteria included positive hepatitis B e antigen (HBeAg); alanine aminotransferease (ALT) > or = 1.5 x upper normal limit, but < or = 10 x upper normal limit; positive HBV DNA; absence of cirrhosis; treatment naivety and no co-morbid factors. A total of 98 HBeAg-positive patients were recruited, of which 48 were randomized to combination therapy and 50 to monotherapy. The primary endpoint was the loss of HBeAg at 72 weeks. The secondary endpoints were HBeAg seroconversion, normalization of ALT, loss of HBV DNA and improvement in histology. The HBeAg loss was 45.8% and 28.0% for combination therapy and monotherapy, respectively (difference, 17.8%; 95% CI -1.2%-35.3%, P = 0.067). There was a trend towards HBeAg loss when using combination therapy. There were also no statistically significant differences between the different therapies with respect to the secondary endpoints of HBeAg seroconversion, changes in histology, normalization of ALT or loss of HBV DNA. In conclusion, this trial showed a 17.8% improvement in HBeAg loss rates using combination therapy over interferon monotherapy. This could clinically indicate a potential important difference that would need confirmation in subsequent trials.