[en] In organic samples there are interfering secondary reactions due to their hydrogen, oxygen and carbon contents in the case of fast-neutron activation analysis which is the most suitable nuclear method for nondestructive determination of nitrogen in various matrices. The yields of these reactions have been studied in a wide range of O/H and C/H ratios. Irradiations were performed with 14.5 MeV neutrons. The induced N-13 activity was measured with a Ge(Li) detector. Cellulose nitrate foils served as flux monitors. (T.I.)