When diffusion techniques are used to prepare samples for 15 N analyses, low or variable N recovery is sometimes observed. The effect of low recovery on estimates of 15 N enrichment is unknown. Also, the suitability of diffusion techniques for use with a variety of salt solutions and digests containing very low N concentrations (92% recovery of 50 µg NH +4 ‐N from 75 mL of 2 M NaCl, total Kjeldahl digests, or 2 M KCl preserved with acid. Leaving sample containers open for 5 d after diffusion for NH +4 completely eliminated contamination of NO −3 ‐N by residual NH +4 ; however, recovery of NO −3 was inversely related to the length of the open period. Recovery of NO 3− ‐N from 0.5 M K 2 SO 4 and alkaline persulfate digests after a 3‐d open period was 90 and 77%, respectively. Complete recovery of NH +4 or NO −3 was not required to obtain accurate estimates of 15 N enrichment; however, when recovery was 15 N enrichments, diffused standards often had 15 N enrichments that were significantly different from nondiffused standards; however, when the mass of N in blanks was estimated using an isotope dilution equation, there was excellent agreement between diffused and nondiffused standards, regardless of the degree of recovery.