A method is described for the simultaneous determiantion of plutonium-241 and plutonium alpha-activity. The plutonium is isolated by coprecipitation on barium sulphate followed by extraction into di(2-ethylhexyl)-phosphoric acid, which is incorporated in a liquid scintillator for counting in a liquid scintillation spectrometer. Interferences from alpha- and beta-emitting radionuclides are studied together with interferences from non-radioactive elements. The lower limit of detection is in the region of 1 pCi.