If in vitro tools can be used to predict which renal transplant patients are at risk for rejection and which patients are more predisposed to tolerance, the immunosuppressive regimen can be adjusted to prevent rejection before it becomes clinically apparent or, in case of a tolerant patient, medication can be reduced or even stopped. Peripheral blood mononuclear cells (PBMC) of patients with persistent stable graft function and of patients with (biopsy-confirmed) acute rejection were stimulated with donor cells and tested with Elispot analysis. A significantly higher number of donor-specific interferon (IFN)-gamma producing cells were found in patients with rejection, as determined with Elispot analysis. Furthermore, a trend towards a higher number of interleukin (IL)-10 producing cells was found in patients with stable graft function. The ratio of IFN-gamma/IL-10 producing cells showed to be the best tool to discriminate between nonrejecting patients and rejecting patients.