[en] Development and practical application of a method for the extraction of Pu with tridodecylamine (trilaurylamine, TLA) from nitric acid solutions of soils and plant ashes are described. Pu is converted into its tetravalent form and extracted with a 25% TLA/xylene mixture from 7 N HNO3; the major part of Th is removed by means of washings with 10 N HCl and Pu backextracted with dilute HCl/HF followed by electrodeposition of the element from acidic ammonium chloride solution to obtain a preparation suitable for α-spectrometry. Some results of the analysis of soils and plant material are given. (author)