A single posttransplant test for human leukocyte antigen (HLA) antibodies in heart and lung graft patients was examined for its predictive value for graft survival as part of the 13th and 14th international histocompatibility workshops. We included patients with HLA antibodies who were tested 6 or more months after transplantation. They were followed for 3 to 5 years. Kaplan-Meier survival curves were used to analyze the data. Of the 235 heart transplant patients, 24.7% had HLA antibodies, whereas 13.3% of the 150 lung transplant recipients, tested positive for HLA antibodies. Heart transplant patients with antibodies had a 5-year survival of 42% vs. 58% for those without antibodies (P=0.0065). For lung transplant patients, the 5-year graft survival was 27% for those with antibodies vs. 56% for those without (P<0.0001). These results indicate that for heart and lung transplant patients, a single test after transplantation of HLA antibodies is predictive of graft survival.