After renal transplantation, acute allograft dysfunction secondary to acute rejection occurs in around 30-40% of patients. Although in the majority of patients these episodes are reversible, acute rejection remains a major risk factor for the development of chronic rejection. Remarkably, prior episodes of acute allograft rejection are associated with decreased allograft survival. Histologic examination of the percutaneous core needle transplant biopsy remains the gold standard for the diagnosis of acute rejection. It does, however, have a number of shortcomings, and less invasive procedures that could diagnose incipient rejection and simultaneously provide mechanistic information on the rejection process (allowing delivery of more tailored therapy) are being sought. To address these problems a number of alternative diagnostic procedures have been suggested, including duplex Doppler ultrasound assessment, fine-needle aspiration biopsy, urine cytology, urine cytokine analysis, serum cytokine analysis, and cytokine analysis of biopsy material.