An attempt to analyse the nucleation and growth phenomenon in a typical "Stranski-Krastanov" (SK) growth system -Ag/W (PAUNOV, MICHAILOV 1979; MICHAILOV), in terms of island growlh theory was made. Ag-layers were analysed by the use of scanning electron-and optical microscopes. A strong dependence of the nucleation kinetics on supersaturation and grain orientation was found to exist.On the basis of known rate equations, the number of atoms in the critical cluster i and the value of nucleation potential barrier E were estimated. The comparison between the experimentally obtained size-, first nearest neighbour-and radial distributions and theory shows that: 1) nucleation and growth processes proceed through a surface diffusion of the atoms; 2) no coalescence between the crystallites and no crystal mobility exist.