We compared two solution hybridization assays, the AffiProbe assay (Orion Corporation) and the Abbott HBV-DNA assay (Abbott), for quantitative measurement of hepatitis B virus (HBV) DNA in serum samples obtained from chronic hepatitis B surface antigen (HBsAg) carriers. Forty transversally collected (group 1) and 83 serially collected (group 2) serum samples from chronic hepatitis B patients were tested with both assays. The serial serum samples were obtained from 6 patients who underwent alpha-interferon therapy with different outcomes (nonresponse, hepatitis B e antigen [HBeAg] seroconversion, HBeAg and HBsAg seroconversion). In group 1 a good correlation (r = 0.91; P < 0.001) was found between the HBV-DNA results of the two assays. Two samples (5%) were HBV-DNA positive according to the Abbott but negative according to the AffiProbe assay; for all other samples the HBV-DNA status corresponded. In group 2 the assays gave colinear HBV-DNA results during follow-up of 5 of the 6 patients (correlation for the total group: r = 0.90; P < 0.001). Nevertheless, in both groups the AffiProbe assay yielded about 5-10 times higher HBV-DNA levels than the Abbott HBV-DNA assay (P < 0.001). These discordant results were most probably due to standardization differences of the positive control samples of the two test systems. This observation underlines the need for international standardization of HBV-DNA and uniform reference panels.