A method has been developed for the substoichiometric extraction of copper with a solution of α-benzoinoxime in chloroform. The separation can be carried out in the absence or in the presence of tartaric acid at pH 6.8–7.0 and 9.5, respectively. In the presence of tartaric acid no interference has been observed. The method has been applied to the determination of copper in biological material, silicon, aluminium and kaolin by the neutron activation method.