The woodchuck (Marmota monax) model infected with woodchuck-specific hepadnavirus (woodchuck hepatitis virus) has proven to be an important model to: ? Study pathogenesis (viral hepatitis, hepatocellular carcinoma); ? Assess efficacy and safety of antivirals for hepatitis B and D; ? Understand and target host responses to infection, protection, and viral resolution;and ? Study the comparative natural history of viral infections in woodchucks compared to humans. Testing in vivo may include obtaining samples of pharmacokinetic analysis, assessment of toxicity, dose escalation, immunostimulation, and efficacy of mono therapies and combinations of therapies.