A soil test to accurately predict the amount of nitrogen (N) mineralized in a given year would be of great value to those involved in production agriculture and those concerned with environmental degradation due to over-fertilization of crops. The primary crop of interest is corn (Zea mays) since annually this crop receives the majority of the applied nitrogen fertilizer. The past few years has seen a great deal of interest in the Illinois soil nitrogen test (ISNT) developed at the University of Illinois. This test is based on the finding that the amino sugar-N content of a soil is a good indicator of N mineralization. The test measures the amount of amino sugar-N and ammonium-N released when soil is heated following treatment with sodium hydroxide. While early results from Illinois showed very positive results for this test, recent results from Wisconsin, Iowa, Michigan, and other states suggest that the test is not useful for predicting corn N response. In Wisconsin, the ISNT has been evaluated in more than 20 cropping experiments that include various cropping and management histories over a 20-year period. In selected studies, soils were subjected to the organic N fractionation procedure used to develop the ISNT. This method provides estimates of the amino sugar-N, amino acid-N, ammonium-N, and total hydrolyzable-N in the soils studied. From this data, we hope to quantify the forms of soil N measured by the ISNT and to gain information on why the test does not provide a reliable estimate of plant available N as originally expected.