Abstract A Carlo Erba elemental Analyzer interfaced to a Finnigan MAT Delta mass spectrometer and a MAT CH-4 mass spectrometer equipped with a thermostated gas-inlet system were used in a comparative study of the 15N/14N ratios of pea powder and an ammonium sulphate standard with 0.93% and 1.34% 15N, respectively. The samples were measured on-line with the Delta instrument, whereas the CH-4 instrument required a Kjeldahl digestion followed by oxidation of the ammonium ion to nitrogen in glass ampoules. The results obtained by the two methods for the ammonium standard were identical within experimental error (0.1% relative standard deviation). The pea powder gave a slightly higher 15N value with the on-line method. Well-defined samples of pea powder are available for reference material purposes.