An improved procedure and a new extraction apparatus for determining soluble nitrogen in feedstuffs are presented. This equipment was used to compare the quantity of nitrogen extracted from seven feedstuffs by several mineral solvents and autoclaved rumen fluid. The quantity of nitrogen extracted by either a modified Burroughs mineral mixture of McDougal's artificial saliva differed from that extracted by autoclaved rumen fluid, whereas that extracted by either Burroughs mineral mixture or by sodium chloride solutions did not. Within solvents, the effects of ionic strength (.11, .15, and .19) and ionic species were studied. Changing the ionic strength of the solvents had no significant effect on the quantity of nitrogen extracted. There were several feed-solvent interactions, suggesting that ionic species contained in the solvent have an important effect on nitrogen extractions. Soluble nitrogen values of six feedstuffs obtained with each mineral solvent were correlated with free ammonia values from incubating each feedstuff with an 80% viable rumen fluid-20% McDougal's artificial saliva solution. Relationships were not consistent.