Nucleation in a superheated gas-saturated solution is regarded as a diffusional process in the space of three variables of a nucleus: Its volume upsilon and the partial pressures of the components p(1)",p(2)". The paper determines the surface relief of the thermodynamic potential in the vicinity of the saddle point and describes the growth of vapor bubbles in a solution with allowance for its viscosity, rate of evaporation of molecules of a solvent, and a dissolved substance, rate of diffusional supply of a substance to the bubble surface. The tensor of the generalized diffusion of nuclei, the decrement of increase of an unstable variable, the stationary nucleation rate have been calculated.