This project aims to devise a novel LC-MS/MS assay with isotopic internal calibration for the measurement of metabolic precursors of oxalate in urine. Urine oxalate is increased in the primary hyperoxalurias, which are a group of inherited disorders of endogenous oxalate overproduction. Patients suffer from nephrocalcinosis and recurrent stones, which can lead to renal failure in the most severe cases. There are three types of primary hyperoxaluria and the pattern of oxalate metabolites in the urine can be helpful in their differential diagnosis. Implementing a urine oxalate metabolite LC-MS/MS assay with isotopic internal calibration will allow patients to be diagnosed faster than current methods. Use of internal calibration rather than calibration curves will also make the assay significantly cheaper for the department.