[en] Procedures for determination of plutonium and americium isotopes in the three main sea components: water, bottom sediments and biota are described. In general, the methods consists of four stages: pre-treatment, chemical separation, source preparation and alpha-particle measurements. Depending on material which is analyzed, the pre-treatment is performed by use of coprecipitation, dry ashing, wet mineralization and acid leaching. For americium and plutonium separation from other anions and cations, ion-exchange chromatography, liquid-liquid extraction and coprecipitation are applied. The measurement samples are prepared by electrolytic deposition of separated elements or by transferring americium and plutonium previously coprecipitated with neodymium fluoride, onto membrane filters. Alpha-particles measurements are performed by α-spectrometry method with application of barrier surface silica (Si/Au) detectors or passivated implanted surface silica (PIPS) detectors. The choice of the needed procedure depends on the analyzed samples. In above described methods the lower detection limits for plutonium and americium are from 0.02 to 0.4 mBq/sample at measurement time in the range of 1400 to 10000 min. The final recovery ranged from 30 to 100%. The radiochemical separations followed by a spectrometry measurements are the only possibility for determination of plutonium and americium in the marine low activity environment samples. (author). 23 refs, 4 tabs