The members of the mono-amino-dicarboxylic acid series were slightly more nitrifiable in a soil medium than those of mono-amino-mono-carboxylic acid series. Diamino-mono-carboxylic acids appear superior in nitrifiability not only to the above 2 series but also to heterocyclic amino acids, which are slightly better than the dicar-boxylic acids. Brucine and strychnine have shown least nitrification values; nicotine and arginine, the greatest. None of the nitrogenous organic compounds compare with (NH4)2SO4 in nitrifiability. Xanthine and uric acid are easily nitrified. Ring N resists soil microorganisms more than chain N. Therefore the nitrification of pure nitrogenous organic compounds is in some measure correlated with composition and properties. The compounds containing a larger percentage of N in their molecules produce larger amounts of nitrates. Organic compounds of N having more complex formulas than the mono-amino-carboxylic series show some relation between the nitrification values and the C:N ratios.