Detection of hepatitis B virus DNA by polymerase chain reaction in plasma of volunteer blood donors negative for hepatitis B surface antigen. Plasma samples from 206 volunteer blood donors were tested for hepatitis B virus (HBV) DNA by dot blot hybridization and polymerase chain reaction (PCR). All donors were negative for hepatitis B surface antigen (HBsAg) and had normal serum alanine aminotransferase levels. None of the 206 plasma samples was positive for HBV DNA by dot blot hybridization assay. However, nine samples were positive for HBV DNA by PCR using two primer pairs specific for surface and core regions. Nine persons received the HBV-DNA-positive plasma, and one developed posttransfusion non-A, non-B hepatitis; the others remained well 6 months later. Therefore, approximately 4% of blood donors in Taiwan have low titers of HBV DNA, and a more sensitive method to screen donors may be needed in the future, although the current serologic test remains the most practical at present. 