Abstract: An oxalate oxidase can be extracted from the stems of beet by homogenizing the beet, filtering, centrifuging the filtrate, precipitating the oxalate oxidase containing fraction with acetone, dissolving the precipitate in taurodeoxycholic acid, dialyzing the solution and column chromatography. Unlike prior art oxalate oxidase compositions, the instant composition is relatively insensitive to sodium chloride and is well adapted to rapid and inexpensive oxalate assay in body fluids. The composition is inactive on almost all body fluid components other than oxalate, the only significant interfering component being ascorbate, and this ascorbate is readily removed by treatment with acid ferric chloride prior to the oxalate oxidase assay procedure, the ferric ion being thereafter removed by a cation exchange resin.