Soils are capable to consume N<sub>2</sub>O. It is generally assumed that consumption occurs exclusively via respiratory reduction to N<sub>2</sub> by denitrifying organisms (i.e. complete denitrification). Yet, we are not aware of any verification of this assumption. Some N<sub>2</sub>O may be assimilatorily reduced to NH<sub>3</sub>. Reduction of N<sub>2</sub>O to NH<sub>3</sub> is thermodynamically advantageous compared to the reduction of N<sub>2</sub>. Is this an ecologically relevant process? To find out, we treated four contrasting soil samples in a flow-through incubation experiment with a mixture of labelled (98%) <sup>15</sup>N<sub>2</sub>O (0.5–4 ppm) and O<sub>2</sub> (0.2–0.4%) in He. We measured N<sub>2</sub>O consumption by GC-ECD continuously and δ<sup>15</sup>N of soil organic matter before and after an 11 to 29 day incubation period. Any <sup>15</sup>N<sub>2</sub>O assimilatorily reduced would have resulted in the enrichment of soil organic matter with <sup>15</sup>N, whereas dissimilatorily reduced <sup>15</sup>N<sub>2</sub>O would not have left a trace. None of the soils showed a change in δ<sup>15</sup>N that was statistically different from zero. A maximum of 0.27% (s.e. ±0.19%) of consumed <sup>15</sup>N<sub>2</sub>O may have been retained as <sup>15</sup>N in soil organic matter in one sample. On average, <sup>15</sup>N enrichment of soil organic matter during the incubation may have corresponded to a retention of 0.019% (s.e. ±0.14%; <i>n</i>=4) of the <sup>15</sup>N<sub>2</sub>O consumed by the soils. We conclude that assimilatory reduction of N<sub>2</sub>O plays, if at all, only a negligible role in the consumption of N<sub>2</sub>O in soils.