A review of more than 3000 cadaver donor renal allograft recipients transplanted between June 1977 and July 1982 as part of the South-Eastern Organ Procurement Foundation (SEOPF) Prospective Study was performed to identify patients who received a transplant following a significant decrease in pretransplant sensitization as measured by the percentage of panel-reactive antibody (PRA). Such patients were identified as having had a most reactive (historical peak sera) PRA level at least 40 percentage points higher than their last sample tested prior to transplant (current sera). Additional data were obtained on 157 of these patients, who also had no history of pretransplant immunosuppression and had a negative pretransplant crossmatch with current sera. Data included the dates of pretransplant sera samples, the specific techniques used for each serum sample that was crossmatched or screened for PRA, and the serological results. The population studied included 17 of 87 first-transplant recipients and 17 of 70 regrafted recipients whose pretransplant crossmatches with peak sera were positive or not done. These subgroups showed no decrease in graft or patient survival compared with cohorts (70/87 first-transplant recipients and 53/70 regrafted recipients) for whom peak sera crossmatching was performed with negative results. Additional stratification for the techniques used in crossmatching and screening, as well as the interval between peak and current PRA levels, showed no significant associations with eventual graft or patient outcome. These results suggest that crossmatch testing using peak sera may not be important in predicting eventual graft or patient outcome for patients with a marked decrease in PRA prior to transplantation and a negative crossmatch with current sera.