Redevelopment of hepatitis B surface antigen after renal transplantation. A patient with chronic hepatitis B virus (HBV) and chronic renal failure received a renal transplantation. Hepatitis B surface antigen (HBsAg) disappeared, and antibodies to HBsAg appeared 10 months before transplantation. Liver tests showed no abnormality at transplantation. Six months later, chronic hepatitis reactivated, antibodies to HBsAg disappeared, and HBsAg reappeared. Hepatitis B virus DNA was demonstrated with polymerase chain reaction in the serum collected before transplantation. This observation suggests that low level HBV replication was present before transplantation despite the absence of detectable HBsAg and was reactivated under immunosuppressive therapy after transplantation. 