A radiochemical method for the simultaneous determination of ²³⁹Pu +²⁴⁰Pu and ²⁴¹Pu in environmental samples has been developed. In the course of the analysis a ²³⁶Pu tracer was used for estimating the chemical yield of plutonium isotopes. After suitable pre-treatment of the sample, the plutonium nuclides in solution were coprecipitated with iron(lll) hydroxide and calcium oxalate and isolated further from impurities and interfering radionuclides by means of anion-exchange chromatography. Plutonium isotopes in the eluate (NH₄l—HCl) were converted into nitrate form and then extracted with 20 ml of 5% bis(2-ethylhexyl) hydrogen phosphate extractive cocktail. The final organic solution was measured spectrometrically using an ultra-low-level liquid scintillation spectrometer, Quantulus (LKB, 1220 Wallac). The chemical yields of plutonium range from 25 to 50% for 100 l of sea-water and 30 to 60% for 40 g of dried soil sample. The counting efficiencies are nearly 100% for ²³⁹Pu +²⁴⁰Pu and 48.8% for ²⁴¹Pu, respectively. The detection limits were estimated to be 0.20 mBq for ²³⁹Pu +²⁴⁰Pu and 2.2 mBq for ²⁴¹Pu, respectively. The proposed procedure has been tested for the simultaneous determination of ²³⁹Pu +²⁴⁰Pu and ²⁴¹Pu in sea-water (Irish Sea, North Sea) and soils (Cumbrian coast, UK; Byelorussia, USSR).