The new Abbott RealTime hepatitis B virus (HBV) assay was compared to the Cobas AmpliPrep/Cobas TaqMan assay with 128 serum samples from patients with chronic hepatitis B. There was an excellent correlation (r = 0.961) between the two assays, with the Abbott RealTime test showing at least equivalent sensitivity and a slightly wider dynamic range than the Cobas TaqMan assay. By coupling high sensitivity with a large dynamic range, the Abbott RealTime HBV assay is useful in monitoring the response to antiviral therapy.