The aim of the present study was to assess the renal excretion of red beet juice (RBJ) antioxidants in six healthy humans. After a single oral dose of RBJ. The pharmacokinetic parameters obtained from urine were compared to those obtained after ingestion of water on an intra-individual basis. Urine was collected in intervals up to 24 h post-intake. After RBJ ingestion, the betacyanins betanin and isobetanin were excreted in the volunteers’ urine (0.28% of the administered dose) and unambiguously identified by HPLC–ESI-MS/MS. Compared to the ingestion of water, RBJ consumption resulted in a significantly increased urinary excretion of total phenolics (51.1% of the administered phenolics) and other antioxidant compounds (43.9% of the administered compounds) within 24 h.