The radius of a spherical precipitate particle growing in a solid solution of initially uniform composition may be shown to be equal to &agr;(Dt)½, whereDis the atomic diffusion coefficient,tthe time of growth, and &agr;, the growth coefficient, is a dimensionless function of the pertinent compositions. In this paper the precise dependence is found of this function upon the pertinent concentrations. A similar computation is made for the growth coefficient corresponding to the one‐dimensional growth of a plate.