During a period of 4 1/2 years the incidence and clinical course of endemic hepatitis B infection was studied in 43 renal transplant recipients with an observation time of 3 to 47 (average: 26.3) months after surgery. During the investigation period 27 out of 43 patients (62.8 per cent) had hepatitis B infection. In 8 patients HBs antigenaemia persisted after chronic dialysis treatment. After surgery HBs antigenaemia was detected for the first time in 7 patients. Recurrence of HBs antigenaemia was noted in one patient. In 7 further cases with HBs antigenaemia after transplantation regular controls of HBsAg and HBsAb were not available before transplantation. In 2 patients HBs antibodies were detectable at the time of transplantation; 2 further patients developed HBs antibodies postoperatively. Hepatitis B infection showed a mild and persistent clinical course. 6 out of 7 icteric patients simultaneously had other severe mycotic and viral infections. Therefore, the conclusion was drawn that in patients with coexisting multiple infections liver damage is not necessarily attributable to HBs antigenaemia.