[en] Experiments have shown that high resolution gamma-spectrometry, using the intrinsic gamma-rays of Pu-239 at 129 or 414 KeV and U-237 (a daughter product of Pu-241) at 208 KeV, is suitable for the in-line assay of plutonium and uranium in 10 ml samples of both the organic and aqueous phases after solvent extraction. Distribution coefficients for plutonium and uranium (with U-237 as tracer) are measurable with an accuracy of better than +- 5% for an initial aqueous phase plutonium concentration of > 0.5 g/l, provided that the distribution coefficients are within a range of 0.1 to 10, and the amount of U-237 present is equal to that in equilibrium with a plutonium source containing > 0.5% Pu-241. The detection limit for plutonium in 10 ml samples is estimated to be < 0.08 mg Pu using a solid state detector with a relative counting efficiency of > 10%, a source detector separation of about 1 cm, and a counting time of 5 min. The detection limit of uranium as U-235 at 186 KeV in the presence of 100 mg Pu, is estimated to be approximately 0.75 mg U-235 under similar conditions. The detection limit for U-237 in equilibrium with Pu-241 is equivalent to < 0.4 μg Pu-241. (author)