Chronic hepatitis B patients with low pre-treatment HBeAg (and HBV-DNA) levels are more likely to respond to interferon-alpha therapy. In retrospect, this low level of HBeAg may have been reached just before the start of therapy. Pre-treatment changes in HBeAg levels were studied in 121 patients undergoing interferon-alpha 2B therapy. HBeAg was monitored by the AxSYM HBe 2.0 Quantitative (Abbott Laboratories) and HBV-DNA by liquid hybridisation (Abbott Laboratories). At the end of treatment (week 16) 24 patients had responded (HBeAg and HBV-DNA below the level of detection). Response was significantly (P = 0.007) related to a decrease in HBeAg level before the start of therapy. Eight of the 24 (33%) responding patients exhibited a > 50% decrease in HBeAg level just before the start of therapy compared to 7 of the 97 (7%) non-responding patients. The geometric mean titre of HBeAg decreased significantly (P < 0.005; 8-week period before start) among responding patients (271 ( 98 PEI U/ml) in contrast to non-responding patients (737 ( 724 PEI U/ml). Planning the start of interferon treatment just after a spontaneous decrease in HBV replication may increase the response rate for interferon-alpha therapy.