SUMMARYTransformations of sodium acetate, ammonium sulphate, urea and wheat straw in peat have been studied by determining the distribution of15N‐labelled material, and by13C and15N nuclear magnetic resonance spectroscopy (NMR) using cross polarization (CP) and magic‐angle spinning (MAS). Samples of an oligotrophic blanket peat were incubated for 6 months at 15°C with15N ammonium sulphate,15N urea,13C15N urea,15N‐labelled wheat straw or13C sodium acetate. The incubated samples were separated into fractions of>1 mm, 1–0.5 mm, 0.5–0.25 mm, 0.25–0.15 mm, 0.15–0.05 mm, 0.05–0.005 mm and a water‐soluble fraction by wet sieving, and were then freeze‐dried. The distribution of15N between the fractions was obtained after isotope‐ratio analysis by mass spectrometry, and the 0.5–0.25 mm, 0.05–0.005 mm and water‐soluble fractions from the incubations were examined by13C and15N NMR.13C‐labelled acetate increased carbohydrate resonances in the 0.05–0.005 mm and soluble material, but an organic acid derived from the substrate was still present 6 months later. Incorporation of15N from ammonium sulphate into the peat was low, and more than 50% of the added N was detected in the soluble fraction still present as15NH+4. As carbohydrate and soluble organic matter were detected in the peat, it was concluded that microbial activity and N immobilization were restricted by poor aeration and low pH. Urea, in contrast, interacted with all the fractions examined, with some15N being incorporated into a range of compounds that included protein, peptides, amides, amino acids and carbamates or lactam derivatives. A small proportion of labelled15N from wheat straw, orginally present in the>1 mm and 14.5 mm fractions, had moved into the 0.05–0.005 fraction during incubation and sieving. The13C spectra suggested that the presence of the straw may have stimulated de