Renal allograft survival is signficantly worse than average in recipients who have never had blood transfusions. It has been speculated that this might be explained by the fact that patients on chronic dialysis often received plasma protein fraction (PPF) instead of blood and that HLA antigens from serum were likely to present in PPF. We have examined four different lots of both PPF and albumin for the presence of HLA antigens. Using the microlymphocytotoxicity technique, each lot was tested for the ability to neutralize ten different antisera containing antibodies against well-defined HLA antigens. In every case, no inhibition was observed--even when the ratio of blood derivative to antiserum was as high as 256:1. These results suggest that if PPF and albumin do contain HLA antigens, they are present at levels too low to be detected by the cytotoxicity test routinely used in HLA typing.