Hepatitis B infection is relatively common in renal transplant patients. Sources of infection include multiple blood product transfusions, hemodialysis machines, and close contact of the immunosuppressed patient with other dialysis patients. We have recently become aware of another previously suspected, but heretofore unproven, source of hepatitis B virus in these patients - the transplanted kidney. We therefore recommend screening for hepatitis B in all prospective renal transplantation donors. Kidneys from donors with positive HBsAg should not be transplanted into susceptibe (anti-HBs-negative) patients.