The objective of the study was to determine the effect of nitrogen dose and the development phase of spring triticale on nitrogen uptake by that plant from the soil and from a mineral fertiliser enriched with isotope ¹⁵N, produced by Isotec, USA. The coefficients of nitrogen utilisation from the fertiliser by the test plant were calculated with the differential method and the method of isotopic dilution. Spring triticale was cultivated in three fertilisation variants: without nitrogen fertilisation, and with the application of fertiliser doses of 30 and 150 kg N ha^{-1 in the form of ammonium nitrate enriched with nitrogen isotope 15}N. Estimation was made of the content of nitrogen in particular parts of the plants (roots, stems, leaves, flowering ears or chaff, respectively, and grain) in the flowering and full maturity phases of spring triticale. It was found that a larger amount of total nitrogen was taken up by spring triticale fertilised with the dose of 150 kg N ha^-1 than 30 kg N ha^-1, and the uptake was higher in the phase of full maturity than in that of flowering. In the total uptake of nitrogen the share of nitrogen taken up from the soil was higher (average of 72.9%) than of nitrogen taken up from the mineral fertiliser (average of 27.1%). Nitrogen utilisation from the mineral fertiliser by spring triticale, calculated with the method of isotopic dilution and with the differential method was 50.4% and 42.3%, respectively, in the flowering phase and 42.5 and 40.3% in full maturity phase. Nitrogen utilisation calculated with the method of isotopic dilution was higher in the flowering phase than at full maturity of spring triticale, and also higher from the fertiliser dose of 30 kg N ha^-1 than 150 kg N ha^-1. Calculations with the differential method also showed higher nitrogen utilisation after the application of the smaller dose of nitrogen. No significant differences were noted between the values of nitrogen utilisation coefficient for the harvest times of the test crop.