W. Thomas London, Jean Drew, Edward Lustbader and others in our laboratory have undertaken an extensive study of the patients in a large renal dialysis unit in Philadelphia. The renal patients can be characterized on the basis of their response to infection with hepatitis B. Patients who develop antibody to HBsAg are significantly more likely to reject transplanted kidneys that are not completely matched for HLA antigens than patients who become carriers of HBsAg (Fig. 5). Since many of the patients became exposed to hepatitis B while on renal dialysis, their response to infection can be determined prior to transplantation. In this patient population there is a correlation between development of anti-HBs and the subsequent development of anti-HLA antibodies after transplantation. We have also found a correlation between the development of anti-HLA and anti-HBs in transfused hemophilia patients and in pregnant women. Hence, there appears to be a correlation between the response to infection with HBV and the immunologic response to polymorphic human antigens in tissue transplants. Further, from preliminary studies it appears that donor kidneys from males are much more likely to be rejected by patients with anti-HBs than by patients without anti-HBs. These differences were not observed when the kidneys were from female donors. Dr. London is now extending his observations to other transplants, in particular, bone marrow, to determine whether a similar relation exists.