A mathematical model of accelerated solid-state diffusion during mechanical alloying (MA) in a binary substitutional system A-B is developed. An individual lamellar particle formed due to fracturing/cold welding during a preliminary stage of MA is considered. Interdiffusion occurs via the vacancy mechanism. During the plastic deformation, jog dragging by moving screw dislocation generates non-equilibrium point defects (vacancies and interstitial atoms), which can diffuse, interact with edge dislocations and recombinate. To evaluate the point defect generation rate, a simple Hirsch-Mott theory is employed. Numerical simulation has been performed for a repeated "deformation-rest" cycle at 100degreesC using realistic parameter values. The influence of non-equilibrium vacancies on the atomic diffusion is evaluated. It reveals itself via the increase of partial diffusivities of substitutional atoms and through the cross-link terms in the matrix of interdiffusion coefficients. The incoherent phase boundary between parent phases (pure elements) is considered as a sink for non-equilibrium vacancies. Due to interplay of these factors, substantial alloying by solid-state diffusion is observed after a reasonable time of MA (4000 s). (C) 2004 Kluwer Academic Publishers.