At New York Weill Cornell Center, we are in a unique position to attempt immunosuppression minimization due to our ability to non-invasively monitor patients using their urine. Previous investigations performed at this center have demonstrated the diagnostic accuracy of mRNA levels of cytotoxic attack molecules in urinary cells. Preliminary data has shown that during acute rejection, Granzyme B and Perforin are strongly expressed in the urine. The sensitivity of the uPCR test was 88% with a specificity of 79%. All kidney transplant recipients at our center are invited to participate in the research study entitled "The use of urinary PCR test to help detect rejection in kidney transplant patients". In this protocol, serial analyses of urinary cells are performed to determine 1) if changes in mRNA levels will predict clinical acute rejection and 2) if these levels correlate with the presence of subclinical acute rejection. Kidney transplant recipients have serial urinary PCR measurements. In addition, patients undergo protocol biopsies of the transplant kidney at 3, 15, and 36 months after transplant. The biopsies help to show the correlation between the PCR results and the pathology of the kidney. It may also serve to detect rejection when the blood tests or urinary PCR do not show it. In a small subset of patients, urinary gene expression profile of cytotoxic attack molecules was able to predict acute rejection prior to clinical diagnosis by renal allograft biopsy.