Summary. Nine patients with lamivudine-resistant chronic hepatitis B infection who had been treated with adefovir 10 mg/day and had had a suboptimal response but did not have genotypic resistance to adefovir were treated with high-dose adefovir (20 mg/day). The response to the increased dose of adefovir was compared with the response in 15 patients with a suboptimal response who did not receive an increase in the dose of adefovir. The increase in the dose of adefovir did not lead to a significant reduction in hepatitis B DNA when compared with patients maintained on the standard dose. These data suggest that increasing the dose of adefovir in patients with a suboptimal response does not lead to an improved response.