A group of 154 patients on chronic dialysis has been evaluated by DNCB reactivity. Viewed as a group, these patients exhibit a highly significant decrease in immunologic responsiveness in comparison to normal individuals. However, 19% of patients had an immunologic response to DNCB and 12% an irritant response. This pretransplant DNCB responsiveness correlated significantly with subsequent allograft rejection in 71 renal allotransplant recipients. For example, at 1 year after transplantation graft survival was strikingly different: DNCB- patients, 78%; DNCB+ patients, 29%; and DNCB-IR patients; 20%. Pretransplant recall-antigen testing results in 32 patients did not correlate significantly with subsequent transplant results. Serial posttransplant delayed cutaneous hypersensitivity responses in patients with a positive response to a skin test antigen in the pretransplant period suggest possible usefulness of this technique for detecting rejection in the posttransplant period. DNCB skin testing should be performed in all transplant candidates to evaluate host responsiveness and should aid in future patient management.