Treatment of Persistent Viremia (Virus in Blood) in Chronic Hepatitis B Subjects Already Receiving Adefovir Dipivoxil

Inclusion Criteria: * 18 through 69 years of age, inclusive * Chronic HBV infection, defined as positive serum HBsAg for at least 6 months * Active chronic HBV infection with all the following: 1. Currently treated with adefovir dipivoxil 10 mg QD (for at least 24 weeks but not more than 96 weeks) 2. HBeAg positive or negative at screening 3. Plasma HBV DNA \>/= 1000 copies/mL at screening (irrespective of HBeAg status) 4. Serum ALT less than 10 times the upper limit of normal (ULN) 5. Calculated creatinine clearance of at least 70 mL/min using the Cockcroft-Gault formula 6. Hemoglobin at least 8 g/dL 7. Neutrophils at least 1,000 /mm3 * Nucleoside naive except for lamivudine (\>/= 12 weeks of therapy) * Negative serum beta human chorionic gonadotropin * Compliant with adefovir dipivoxil * Willing and able to provide written informed consent Exclusion Criteria: * Pregnant women, women who are breastfeeding or who believe they may wish to become pregnant during the course of the study * Male or females of reproductive potential who are unwilling to use an effective method of contraceptive while enrolled in the study. For males, condoms should be used and for females, a barrier contraception method should be used * Decompensated liver disease defined as conjugated bilirubin greater than 1.5 times ULN, prothrombin time (PT) greater than 1.5 times ULN, platelets less than 75,000/mm3, serum albumin less than 3.0 g/dL, or prior history of clinical hepatic decompensation (eg, ascites, jaundice, encephalopathy, variceal hemorrhage) * Prior use of tenofovir DF or entecavir * Received treatment with interferon or pegylated interferon within 6 months of the screening visit * Evidence of hepatocellular carcinoma (HCC); for example, alpha-fetoprotein greater than 50 ng/mL or by any other standard of care measure. * Co-infection with HCV (based on serology), human immunodeficiency virus (HIV), or hepatitis delta virus (HDV) * Significant renal, cardiovascular, pulmonary, or neurological disease. * Received solid organ or bone marrow transplantation. * Is currently receiving therapy with immunomodulators (eg, corticosteroids, etc.), investigational agents, nephrotoxic agents, or agents capable of modifying renal excretion * Has proximal tubulopathy * Known hypersensitivity to the study drugs (tenofovir DF or emtricitabine/tenofovir DF), the metabolites (tenofovir or emtricitabine) or formulation excipients