A positive crossmatch due to T-cell reactivity against donor cells is considered a strong contraindication to renal transplantation because of the risk of graft loss from rejection. However, the significance of T-cell reactivity before but not at the time of transplantation is unknown. To determine whether transplantation can be successful under these circumstances, graft survival was observed in 15 highly sensitised patients whose T cells were reactive to donor sera before but not at the time of transplantation. All patients have been followed up for at least 1 year post transplant. Immunosuppression was by azathioprine, prednisone, and rabbit antithymocyte sera. 9 (60%) have functioning grafts and a mean serum creatinine of 1.6 mg/dl. Early non-function occurred in 12 patients. One graft was lost to early acute humoral rejection and two other to chronic rejection. 14 of the 15 had a fall in reactivity to a panel of normal lymphocytes before transplant. 4 of the 15 had donor-specific B-cell antibodies at the time of transplantation and 3 of these lost their grafts because of rejection.