Chemical Laboratories, University of Allahabad, Allahabad Received 17 February 1972 Equilibrium distributon measurements of copper (II) at three constant ionic strengths (0.1, 0.5, 1.0 M, NaNO3 ) as a function of nitroso-R-salt (NRS) with a number of cation exchangers have been studied and compared with the distribution of free metal ions. The monocomplex of copper does not exchange in the case of Dowex 50W-X12, while exchange occurs with Dowex 50W-X8 and -X4. Stepwise formation constants of the complex species in aqueous phase were computed to be log K1 \(^{\mu = 0}\) and log K2 \(^{\mu = 0}\) as 8.63 and 5.70 respectively at 30°.