Studies were conducted on a 15 N‐labeled Weirdale loam, a Dark Gray Chernozemic soil (Boralfic Boroll) to (i) determine the amounts of N released by several methods previously used to obtain an estimate of potentially mineralizable N, (ii) determine their 15 N enrichment and extractability ratios, and (iii) compare the results from the above with the N mineralized during incubation and NH +4 released by the chloroform fumigation incubation technique. The NH +4 ‐N accumulated during 10 d in fumigated soils accounted for ∼1% of total N, was highly labeled, and had extractability ratios of 6.6 to 7.4. These ratios were similar to ones obtained for N mineralized during incubation of unfumigated soils. Ammonium‐N extracted with dilute acidic permanganate solution (0.01 M KMnO 4 in 0.1 or 0.5 M H 2 SO 4 ) accounted for 0.72 to 0.84% of total N and had extractability ratios ranging from 3.4 to 3.9. A stronger solution of acidic permanganate extracted more N that was less enriched. Dilute sulfuric acid extracted NH +4 and organic N that had extractability ratios of < 3. Ammonium‐N released by autoclaving the soil accounted for ∼1% of total N and had extractability ratios ranging from 0.6 to 0.9. Acid hydrolysis showed that 72% of total N was hydrolyzable, 32% was amino acid‐N and 20% was NH +4 released on hydrolysis. The extractability ratio for NH +4 released on hydrolysis was 1.7 and was significantly ( P < 0.01) greater than extractability ratios of hydrolyzable N and amino acid‐N. The similarity and high extractability ratios of NH +4 released after fumigation and NO ‐3 ‐N accumulating during aerobic incubation indicated that the fumigation extracted a biologically meaningful fraction. The biomass was responsible for only 15 to 25% of the net N mineralized during a 12‐week incubation. Results indicated that (i) extraction of a highly labeled N pool in soil can only partly explain the source of N being mineralized, (ii) N is mineralized from several pools, and (iii) there is a remote possibility that a single extractant can extract the variety of N compounds undergoing mineralization and immobilization in soil.