To investigate the potential influence of grapefruit juice on urinary risk factors associated with the formation of calcium oxalate kidney stones as the product might effect the chemical composition of urine. Rats were rendered nephrolithic by providing drinking water containing 0.75% ethylene glycol (v/v) (EG) and 2% ammonium chloride (w/v) (AC) for 10 days. In addition to EG/AC treatment, three groups of rats were also gavage-administered solutions containing 100%, 75% and 50% grapefruit juice (v/v) (6 µl solution/g body weight). Positive control rats were treated with EG/AC but not grapefruit juice. Negative control rats were provided with normal drinking water and were administered normal water by gavage. Each group contained 6 rats. After 10 days serum samples were collected for analysis, the left kidney was removed and assessed for calcium levels using flame spectroscopy and the right kidney was sectioned for histopathological analysis using light microscopy. Analysis showed that the rats treated with EG/AC alone had higher amounts of calcium in the kidneys compared to negative control rats. This EG/AC-induced increase in kidney calcium levels was inhibited by the administration of grapefruit juice. Histology showed that rats treated with EG/AC alone had large deposits of calcium oxalate crystals in all parts of the kidney and that such deposits were not present in rats also treated with 100% or 75% grapefruit juice.