Hepatitis B virus-DNA was detected by polymerase chain reaction in 9 out of 10 patients after orthotopic liver transplantation. Three of these patients were at the same time positive for hepatitis B virus-DNA by dot-blot hybridization (hepatitis B virus-DNA > 1.5 pg/ml). In these three patients HBs-antigen (HBsAg) reappeared within a mean time of 12 weeks after orthotopic liver transplantation (range 7-18 weeks). Only two of the six polymerase chain reaction-positive and dot-blot-negative patients (hepatitis B virus-DNA between 0.4 fg/ml and 1.5 pg/ml) had recurrence of HBsAg within a mean time of 54 weeks (range 52-56 weeks). Passive immunoprophylaxis with anti-HBs antibodies (serum titers > 100 IU/l) did not prevent infection of the graft in the five reinfected patients. We conclude that a low concentration of serum hepatitis B virus-DNA after orthotopic liver transplantation, which is detectable only by polymerase chain reaction, indicates a delayed infection of the graft.