A new model of the electrochemical alloy deposition has been developed. It is based on the application of the finite Markov chain theory and is called the Markov chain model. The first analytical relationship between the alloy composition (ratio of mol fractions x(A)/x(B) and the metal ion concentrations in the electrolyte (mol fraction X-A and X-B can be deduced from the model. X-A/X-B = X-A(g(A)X(A) + X-B)/X-B(g(B)X(B) + X-A) The general parameters of this equation are the ratios g(i) = K-ii/(ij) of the equilibrium constants between the electrolyte ions and the different kink site positions on the surface (i, j representing the different components of the alloy). It is shown that the gi values can be evaluated by the linearization of the deduced equation. The model was tested according to the literature [K.C. Belt, J.A. Crosley, R.J. Kendrick, Proceedings of 7th International Metal Finishing Conference, Hanover 1968 (data cited in Ref. [17])] by comparison of the calculated and the experimentally determined Co-Ni alloy composition and its dependence on the ion concentration in the electrolyte. The gi values are of primary importance for the quantitative analysis of the mechanism of electrochemical alloy deposition and for the control and prediction of the alloy composition. (C) 2005 Elsevier Ltd. All rights reserved.