Sensitized patients may reject renal transplants at a tempo or with a force dictated by their previous exposure to alloantigen. The patient's pretransplant alloimmunization status is usually assessed by the measurement of panel reactive antibodies (PRAs) and by the crossmatch. The test results using current patient's sera are of considerable predictive value. In contrast, the relevance of historical sera is much debated. To further investigate the correlation of PRA and crossmatch with clinical outcome, 852 cadaveric kidney transplants were evaluated. As expected, graft survival was significantly longer (p = 0.01;logrank test) in nonimmunized patients (n = 516) compared to immunized patients with more than 10% PRA (n = 297). Patients with persistently positive PRAs (n = 171) were then compared to patients with positive historical but negative current PRAs (n = 126). Interestingly, their graft survival was practically identical. Finally, transplants across a positive historical T cell crossmatch (n = 39) had a significantly reduced graft survival (p = 0.015) compared to transplants in immunized patients (n = 297, all T cell crossmatch negative). Thus, this study confirms the increased risk in sensitized patients and shows that the antigen specific immunological memory is of clinical relevance even if donor specific antibodies are not detectable in current sera.