The basic principles of constructing a stochastic computer model of intergranular adsorption kinetics controlled by interatomic pair interactions and the volume diffusion mobility of the components of a solid solution are developed, allowing for the bulk structure of crystals and the equilibrium atomic configuration of intergranular boundaries. The results are presented from computer simulations of the grain boundary segregation of S and P in α-Fe-based alloys. © 2018, Allerton Press, Inc.