Only a few plants contain sufficient amounts of sodium and potassium oxalate to be considered toxic. Moreover, ruminants that consume these plants develop increasing amounts of tolerance to oxalate. An oxalate degrading anaerobe microorganism has been isolated from pure culture of rumen bacteria. This organism, Oxalobacter formigens, uses oxalate as a sole energy source and produces carbon dioxide and formate as end products. This ability is extremely rare among anaerobic bacteria and therefore this organism occupies an unique niche in the rumen's microflora. The ability of the ruminant to adapt and tolerate high oxalate diets directly depends on the selection of oxalate- degrading microorganisms.