Renal rejection is associated with an active immune response regulated by cytokines and in which immunocompetent cells are involved. Previous studies have measured high levels of cytokines in the urine and plasma in various renal dysfunction states. However, some methods used to measured cytokines hinder their use as a diagnostic tool in renal rejection. In this report, cytokine levels were determined in the plasma and urine of kidney transplant patients, with renal rejection and without it, using a cytometric bead array (CBA) technique. Concentrations of six human cytokines (IL-2, IL-4, IL-5, IL-10, TNF-alpha and INF-gamma) were established. Results show that patients who develop renal rejection presented high levels of IL-10 and IFN-gamma cytokines in plasma and urine compared to patients without renal rejection. The CBA technique displayed greater sensitivity in the determination of cytokines in urine than the conventional ELISA technique. Finally, when standard cytokines in plasma and in urine were compared, it was observed that, in plasma, levels of IL-4, IL-5, IL-10, TNF-alpha and IFN-gamma were detected, whereas in urine the levels detected were of IL-4, IL-5, IL-10 and IFN-gamma. These results indicate that the CBA assay is a sensitive method to measure cytokines in urine. In kidney transplant patients undergoing acute renal rejection, the presence of cytokines in urine reflects renal damage and could be a useful method in the diagnosis of renal rejection.