The buffered incubation medium used in many in vitro ruminant feedstuff degradation assays is essentially that described by Goering and Van Soest [1970]. Hungate [1966] suggested that the actual composition of the inorganic salts in the medium was not vital as long as it provided sufficient buffering capacity and was of a similar osmotic potential to rumen fluid, while Tilley and Terry [1963] argued that sufficient trace elements and “growth stimulants” would be provided by the rumen fluid inoculum or substrate and that fermentation gas would maintain anaerobic conditions. The divergent composition of these media reflects that the microbiologists were attempting to create a “habitat-simulating” media [Hungate, 1966] while nutritionists were using a slightly modified rumen environment in vitro to permit microbial degradation of feedstuffs. The objectives of this study were to identify whether reduction of media is necessary prior to use, and to develop a nitrogen free media which could be used for determining the effects of nitrogen supplementation on the fermentation of feedstuffs.